Arachnida

ARACHNIDA

THE Arachnida, or, popularly speaking, the Spiders -and their allied forms—from αράχνη, a spider, and eιδos, the form or outward appearance—constitute a well-defined group within the great branch “Articulata” of the animal kingdom, though on one side its boundary lines melt almost insensibly into the Annelides, through the family of acarids— Pentastonιides. Linnaeus and others of the older systema-tists included all Arachnids (as then recognised) under the class Insecta, Lamarck first separating them into a distinct class. A few general remarks, therefore, on the branch Articulata, and its subordinate groups, may be useful, to show the general relations of that under consideration.

As distinguished from the Vertebrata, the animals of the branch Articulata may be characterised generally as having (besides the marked and uniformly different position of the chief organ of circulation and the nervous chords) an external skeleton, the different parts of which, of more or less solid consistency, are articulated, or jointed to each other, and contain within their hollows the vital and other organs. Internally, threads of nervous matter, springing from enlargements or knots (ganglia) upon two or more central longitudinal nervous chords on the ventral side of the body traverse the different parts of it; these chords, however, end in no one special mass, corresponding to the brain in the Vertebrata; and the nervous systems composed by these ganglia vary considerably in their special structure and arrangement in the different subordinate groups.

This being the distinctive plan of structure in the Articulata, a review of the whole group shows us that this plan is carried out in two well-marked leading ways—first, without, and secondly, with, articulated legs, or organs of locomotion and touch. Those without articulated limbs constitute the Annelides of Lamarck, which, for our present purpose, it is sufficient to characterise as having the articulate plan of structure carried out in the general form of a more or less cylindrical, lengthened body, composed of a number of rings, segments, or transverse folds, of which the first forms the head, but destitute of articulated limbs. Those ' τoith articulated legs constitute the Condylopa of Latreille, or the Insecta of Linnaeus; but the term Insecta being now in general use to define a subordinate group, it will be better to adopt here the name given by Latreille. In the “Condylopa,’’ then, the articulated plan of structure is carried out in the form of a more or less hard body composed of different pieces, of which one, two, three, or more, are generally leading ones; to this body (in general to the anterior portion of it) are attached articulate organs of locomotion various in number, but never, or at least very rarely, less than six. The organs of sight (when present) are always in the head, and vary in number, position, and kind. To these two leading divisions of the branch Articulata—the Annelides of Lamarck, and the Condylopa of Latreille—we may give the designation of Classes, since they are each respectively composed of animals which thus primarily and markedly differ in the way in which their common articulate plan of structure is carried out

Leaving now the class Annelides, to which has been given the name “Anarthropoda,” and confining our attention to the “Condylopa,” or “Condylopoda” (equivalent to the “Arthropoda” of more modern authors), we find that the latter contains the four following groups— a Insecta f “Myriapoda,” “Arachnida,” and “Crustacea.”

These all agree in the way in which, as above explained, their general articulated plan of structure is carried out, but they differ in the f urther modifications of this plan, that is to say, in the number, division, and size (both absolute and relative) of the different articulations of the body (including the organs of locomotion, of manducation, and of touch), and in the respective value and relation of these to each other, as well as in the modifications of their respiratory and other internal systems, and also in other important points. Differing thus from each other, these four groups, usually (three at least of them) ranked as distinct classes, yet appear to be entitled only to the rank of sub-classes, being each merely an equally subordinate group of the class “Condylopoda."

The four sub-classes of Condylopoda (or articulate-legged Annulosa) may be separately and briefly characterised thus :— Sub-class I.— Insecta : subject in general to metamorphosis, more or less complete, during the progress to maturity; organs of locomotion, six; body divided into three principal parts— car>ut, thorax, and abdomen; respiration wholly tracheal.

Sub-class II.— Myriapoda : not subject to metamorphosis, properly so-called; organs of locomotion above six in number (twenty-four and more) developed by degrees, and affixed to the abdominal as well as to the other (numerous) segments into which the body is divided. Although occasionally some of the anterior segments coalesce, and the head is stated to be formed by five or more modified segments, yet no one or more parts of the body can be said to be principal ones; respiration is tracheal.

Sub-class III.— Arachnida : not subject to metamorphosis, properly so-called, though, as with the Myriapoda, some portions of structure among certain acarids, and to a small extent even among the Araneidea, are progressively developed at the various moultings of the skin. Organs of locomotion, eight; body in general divided into two principal parts, cephalo-thorax and abdomen; but where (as in some groups) the abdomen is divided into more or less distinct segments no organs of locomotion are ever attached to them; respiration, where distinct organs exist, is either tracheal, pulmo-branchial, or the two coexistent.

Sub-class IV.— Crustacea: without metamorphosis; organs of locomotion various in number (not less than eight or ten), and attached to some or all of the many segments, abdominal as well as others, into which the body is divided; although in numbers of crustaceans no one part of the body can be called a principal part, yet in some very large and leading groups, the portion covered by the carapace (corresponding to the cephalo-thorax in Arachnids) may well be termed the one principal part; the abdomen being in this case more or less rudimentary or subordinate. Respiration in the Crustacea, where distinct organs are present, is branchial.

In this view the following diagram shows the relative positions of the several leading groups of the Articulata:— [table]

In this diagram the Myriapoda are placed, in the position ordinarily assigned to them, between the Insects and Arachnids; but perhaps a more natural position would be after the Crustacea, for they appear to connect the Insecta and Crustacea more than they do the Insecta and Arachnida. The point, however, of the special position of any large group in a linear series is tolerably unimportant. A linear arrangement is of course the only one possible on paper, but it cannot express the numerous cross relationships that become evident when the affinities of special groups are closely studied. By placing the Myriapoda after the Crustaceans, we seem to get an ascending series in respect to the organe of locomotion: in the Insecta, six—always attached to the thoracic segments; in the Arachnida, eight—almost always attached to the thoracic segments; in the Crustacea, eight, ten, and upwards—frequently attached to the abdominal as well as to the thoracic segments; in the Myriapoda, twenty-four and more—always attached to the abdominal as well as other segments. The relation of the Myriapoda to the Crustacea through the attachment of limbs to the abdominal segments is thus expressed; and by the meeting of the two ends of the line, the always acknowledged affinity of the former to the Insecta is also expressed.

Having thus briefly explained the most obvious relationships of the Arachnida, let us now proceed to a more detailed, though still general, diagnosis of this group. And first, in respect to their external organisation, Arachnids are articulate animals, with eight articulated legs, each in general consisting of seven joints; the head and thorax are soldered together into one piece (cephalo-thorax), from which with few exceptions the legs invariably spring. In one group of the Arachnida (Solpugidea) the cephalothorax is separately segmented, as it is also in one family of the Thelyphonvdea (Tartarides) ∙, the rest of the body forms also one more or less homogeneous piece (abdomen). The abdomen is always more or less closely attached to the cephalo-thorax; in some instances it is soldered to the thorax, and forms with it one undivided piece, in other cases it is only joined to it by a narrow pedicle. At times, also, the abdomen constitutes a simple unsegmented portion, at other times a segmented or annulate portion of the body, occasionally, as in the true scorpions, prolonged into a segmented tail: in one small but very distinct group tfΓhelyphonidea), the abdomen is prolonged into either a simple button, a short jointed, or a more or less long setiform tail · in another large group (Araneidea) the abdomen terminates with organs (spinners and spinnerets) for spinning threads. The eyes (when present) are simple, always sessile, and placed on the fore part of the cephalothorax; they seem to represent the simple ocelli of the Insecta; the large compound eyes of that order having here no representation, the caput of Arachnids appearing to begin at a point posterior to that which bears the antennae and compound eyes of insects. In Arachnida the number of eyes varies from two to twelve. In front of and articulated beneath the fore part of the cephalo-thorax, and moving in different planes in different groups, are two independent, variously modified, organs for seizing and compressing the insects or other substances on which Arachnids in general prey; these organs are often called mandibles, but more generally, and very appropriately, falces : these are considered by some systematists to be the true homologues of the antennae in insects, and to have been derived from those portions of the insect organisation by long and unceasing modification; when, however, the caput of an Arachnid (scorpion or spider, for instance) is compared with that of a coleopterous or hymenopterous insect, in which the mandibles are well developed, there seems far more reason to conclude that the antennae of the insect have no homologue at all in the Arachnid (Claparède, l.c. post), but that the falces of the latter are the true representatives of the mandibles of the former. Behind the falces (and also used in manducation) are two other large movable portions of structure called maxillae; these vary in shape and size, and form in fact lateral and hinder boundaries to the mouth, as well as an apparatus for comminuting and squeezing the food substances; from each of these maxillae, on the outer side, springs a palpus of four or five joints, varying in structure and use. Between the maxillae most Arachnids have also a fixed piece (labium) of various form, completing the hinder limits of the mouth organs, and in some (perhaps in most) there is, within the parts already named, another portion (tongue), not yet sufficiently observed either in regard to its form or use, but probably acting so as to hinder choking. In some Arachni-dans these different parts of the mouth are soldered together and form a tolerably simple sucking apparatus, analogous to the mouth of some insects (Hemiptera, &c.) As observed above, Arachnids are not, in a proper sense, subject to metamorphosis: in most of them there is little real change after they leave the egg; though, in some of the lowest forms, indeed, there are after-changes by moultings of the skin, which approach the incomplete metamorphoses of some insects.

With respect to the internal organisation of the Arachnida, it might perhaps be enough here to refer to the more detailed accounts given further on, where the separate orders are under consideration; but the following summary will probably make our general view of the whole sub-class more complete.

Muscular System. —Of this it is enough to say that it is similar to that of the rest of the Articulata, consisting of flexor and extensor muscles, situated within the hollows of the limbs, besides groups of fibres by which the epidermis and parts within it are connected and held together. On the outer surface these groups frequently show, at their points of union, boss-like marks or foveae, or impressed spots of various forms and sizes, often presenting by their position distinctive peculiarities of form; it is probable that many others of the external specific.markings are dependent on the course and position of the muscular fibres, as well as of the heart and other organs.

Circulatory System.— The vital fluid is circulated by means of an elongated muscular vessel or heart, varying in form, and, instead of being placed, as in the Vertebrata, on the ventral side of the body, extending along the back of the abdomen. This vessel is often divided into chambers or compartments by valves, having also valvular orifices on its upper side for the flowing in of the fluid (Newport), and giving off vessels (arteries) for its distribution to the rest of the body. In the lower forms, however, of Arachnids (among the Aca-ridea) no such principal muscular vessel is found, the vital fluid being in such cases supposed to circulate generally in the body, and to be distributed irregularly into different portions by the muscular movements of the intestinal canal.

Respiratory System.— Arachnids breathe by means of tracheae (spiracular tubes, as in the Insecta), as well as by pulmo-branchiae, said to be a kind of compound of the gill of fish and the lung of mammals, though in reality there seems better reason, as we shall see further on (p. 293), to consider the pulmo-branchiae as merely peculiarly modified tracheae; both these organs have external orifices (stigmata) variously situated, but commonly in some part of the abdomen. In some Arachnids (certain groups of the Araneidea) respiration is effected by both of the above organs; while in others (certain of the Acaridea) no distinct organs of respiration exist.

Digestive System.— Digestion is effected by a simple alimentary tube or canal running from the mouth to the anus. This tube is various in its form, as well as in the intestines issuing from it; in some groups, as the Araneidea and Acaridea, the above canal has large lateral caecal appendages; in others (Scorpionides and Thelyphonides) the alimentary canal has no such lateral enlargements. In some Arachnids there have also been found a liver (or mass of substance in the abdomen exercising the functions of a liver), an organ performing the part of kidneys, and salivary glands, often of large size, while in others no distinct organs of digestion exist.

Nervous System.— This consists of ganglia or nerve-knots, formed by enlargements of longitudinal nervous cords (generally two in number), differing in position and in the nerves issuing from them. In one large group (Acaridea) where the abdomen usurps, as it were, the place of all the rest of the body, there is no longitudinal nerve cord; a single nerve mass occupies the interior of the abdomen, and sends forth nerves to the various surrounding parts.

Generative System.— Generation is effected by two distinct and separate sexes, the single exception known being the Tardigrada , a group of Acaridea approaching nearly to the Entozoa, and said to be hermaphrodite. In females the parts of generation consist of two sacs (ovaria), one on each side of the alimentary canal. These have a common external orifice (vulva), various in its shape, beneath the anterior extremity of the abdomen; and connected with this opening there is frequently an epigyne, or ovipositor, often of some length, and of characteristic form. In males (except among the phalangids and scorpions) there is no intromittent organ,—the generative parts consisting of two long tubes, similarly situated to the ovaria in females, in which the seminal fluid is secreted; these tubes end in a simple external, very minute orifice, in a similar situation to the vulva of the female.

Arachnids are either oviparous or ovo-viviparous. As before observed, they undergo no proper metamorphosis, but as growth takes place there are more or fewer successive moultings of the skin; and complete development of all the parts does not occur until the last moult, when the creature becomes adult, and so fitted to perpetuate its kind.

With regard to the position held by Arachnids in the great scheme of nature, it seems, from the considerations shortly entered into above, undeniable that they are very closely linked to the rest of the Articulata by much, both of external and internal structure, common to the whole branch. The office they subserve is evidently the keeping down of the superabundant supply of the insect world; some even operating to check the too rapid advance of higher animals.

Assuming that the operation, in some shape or other, of evolution has brought the different groups of Articulata to the varied forms and conditions they now respectively present, it is plain that the higher, at least, of the arachnidous orders must, in all probability, have been modified from some one or more of the other groups, perhaps in the main from the Insecta and Myriapoda,— certainly not the Insecta, for instance, from the Arachnida. Thus, we should define Arachnids, generally, to be insects modified for the purpose of preying upon their congeners; while some of the lower forms of Arachnids, such as Demodex, Tardigrada, and Pentastoma, carry us back to the remote past, before the branch Articulata, in any of its great groups, had attained more than a very slight progress towards its present dignified and highly organised forms.

The above being a general summary of the external and internal organisation of the Arachnida, an examination of the whole group shows us that their different characters, and the ways in which their articulated plan of structure is carried out, are variously correlated and modified, forming structural complications of several marked kinds, whence we get the different orders, being the next subordinate groups, into which Arachnids are divided. These orders are seven in number, and form so many well-defined groups, but of very different extent. Advancing from the more simple to the more highly organised, we begin with the Acaridea, comprising the mites and ticks, and including also the Tardigradides, Pentastomides, as well as Demodex. The second order is that of the Pycnogonidea, marine parasites, which, in a certain plane, appear to connect the Acaridea with the next or third order, Phalangidea; these last are popularly known as “Harvest-men.” Next to them, and forming the fourth order, come the Solpugidea, a small but very distinct group, constituting a link in one plane between the Phalangidea and Scorpionidea, which last, including the Chelifers, or False Scorpions, form the fifth order. Not far removed from these is the sixth order, Thelyphonidea, comprising groups which partake of the characters both of the Scorpionidea and of the next— the seventh and last—order. Araneidea. or true Sniders. [table]

The following abstract shows the chief ordinal characters of these seven groups of Arachnids :—

Order I. Acaridea. —Cephalo-thorax and abdomen united so as to form one piece, generally without mark of union; palpi and falces variable in structure; the several parts of the mouth often united; legs terminating variously, generally eight in number, sometimes only six in the immature state, and in one or two instances but four, even when adult; eyes, when present, variable in number (2 to 6), and placed on the cephalo-thorax; respiration, when proper organs for it exist, wholly tracheal; nervous matter gathered into one large mass, or ganglion; reproduction ovo-viviparous as well as oviparous. Maturity is reached by quasi, or imperfect, metamorphoses in some of the groups.

Order II. Pycnogonidea. —Cephalo-thorax segmented, linear; abdomen rudimentary, forming merely a small terminal segment to the cephalo-thorax; the mouth consisting of the termination of a tubular article forming the head, sometimes accompanied by some more or less distinct parts; legs eight, multi-articulate; in females a supernumerary pair, between the first two and used for bearing ova; organs of respiration, none; metamorphosis imperfect, as in the last order.

Order III. Phalangidea. —Cephalo-thorax and abdomen of tolerably equal size, and united throughout their whole breadth, but the junctional line evidently marked; abdomen annulate or segmentate, caused by transverse folds in the epidermis; falces two-jointed, didactyle; legs in general inordinately long, and very slender; the two terminal joints multi-articulate, and ending with, claws; eyes two, on the vertex of the cephalo-thorax; respiration tracheal; reproduction oviparous; no metamorphosis of even an imperfect kind.

Order IV. Solpugidea. —Cephalo-thorax distinct from the abdomen and segmented, the first segment forming the head; abdomen annulate; falees one-jointed, didactyle; palpi terminating with a capsule containing a peculiar organ, the use of which is not yet known; eyes two, on a small eminence at the fore part of the head in the medial line; respiration tracheal; legs'terminating with two curved fingers; manner of progressive growth unknown.

Order V. Scorpionidea. —Cephalo-thorax formed of one undivided piece, united to the abdomen throughout its entire breadth; abdomen annulate, prolonged (in one of the families) into a segmented tail, ending with a poison bulb armed with a sharp perforated point, through which the poison is emitted; falces didactylous; palpi terminating with a didactyle claw; eyes variable in number, two to twelve, variously grouped on the fore part of the cephalo-thorax; respiration, in one family, tracheal, in another, pulmo - branchial; ganglia several, distributed along the nervous chord; reproduction, in some oviparous, in others ovo-viviparous; organs for spinning beneath the fore part of the abdomen in one family; no metamorphosis.

Order VI. Thelyphonidea. —Cephalo-thorax undivided, but its segmental structure generally visible in grooves and furrows, following the course of the soldered joints; abdomen annulate, joined to the cephalo-thorax by a pedicle; palpi very strong, didactylous (in a modified form); falees monodactylous; legs of the first pair excessively long, antenniform, the last joints very fine, multiarticulate, and devoid of a terminal claw; eyes, when present, eight, disposed in three groups on the fore part of the cephalo-thorax; abdomen either terminating with a button-like segment, a short two-jointed tail, or a multi-articulate setiform one; respiration pulmo-branchial; manner of progressive development unknown. In one family, ganglia two, closely united; in others unknown.

Order VII. Araneidea. —Cephalo-thorax undivided, but traces of segmentation commonly more or less visible, united to the abdomen by a narrow pedicle; abdomen without segments or annuli, ending with organs for spinning; falees monodactylous; palpi more or less filiform in males, with the last joint more or less complicated in structure, and used in copulation, terminating in females (but not invariably) with a claw or claws, sometimes pectinated; legs terminating with two or three curved claws, and, except the third (which is rarely so), generally more or less pectinated; ganglia two or three in number; respiration tracheal, as well as pulmo-branchia); reproduction oviparous.

We have thus far obtained a general view of the leading groups of the sub-class Arachnida, both in respect to its relation to collateral groups of equal value, and the relation of its own members to each other, and also a synoptical view of the leading characteristics of the seven orders into which Arachnids may be divided. We now propose to touch shortly, but in greater detail, upon each of those orders, and, as far as our limits will permit, upon the families and genera comprised in them, adding a few general remarks upon each group.

Order I.— Acaridea.

The inclusion in this order of such aberrant forms as Demodex, Pentastoma, and Tardigrada, somewhat destroys its homogeneity; undoubtedly they indicate a passage from the Annelides (Anarthropoda) to the Arthropoda, but whether it would not be more consistent with a strict scientific method to separate the two latter, at least, from the Acaridea, and make each the type of a distinct order, is a point for the future consideration of systematists. At present the balance of opinion appears to be for including them as the lowest transitional forms of the lowest order of Arachnids. With regard to the position of Tardigrada, see Packard’s Guide to the Study of Insects, p. 668, where Claparède is quoted from his Studien an Acariden; also Introduction to the Classification of Animals, Huxley, pp. 123-124, where the position of Pentastomides is also considered. See likewise on this, Cobbold’s Entozoa, part iii. pp. 393-402, where reference is made to Leuckart’s Bau- und Entwicklungsgeschichte der Pentastomiden.

Owing to the excessively small size of most of the Acaridea, and their obscure mode of existence, much of their economy and internal structure is yet unknown. The following is an endeavour to present their characters in somewhat greater detail than in the short abstract given above.

External Structure. —In their general form the Acaridea are more or less round, oblong, or oval; the integument in some is soft, in others coriaceous, and some are quite hard, like a Coleopterous insect.

The cephalo-thorax and abdomen are consolidated into one piece devoid of articulations; not only is the head, as in other Arachnids, soldered to the thorax, but the portion (cephalo-thorax) formed by this union is generally joined invisibly to the abdomen, which is consequently merged in the general covering of the body. In the family Bdellides, however, and also in some other instances, the junctional points of the different parts of the body are visible enough. The legs are eight in number in the mature acarid, except in Pentastoma, which in a state of maturity has none (fig. 1)— the four abnormal-looking legs visible in the young state disappearing in the adult (fig. 2). Many other Acaridea have six legs only until the last moult, when maturity is attained, one or two, even in the adult state, being said to have but four. Each leg consists in general of seven joints, and the tarsi end, in some, with two movable hooks; in others the tarsus is dilated at its extremity as if for feeling with, while in some of those whose habits are aquatic it is expanded; in short, the structure of this part is very various, and adapted to the habits of the different genera. Dugès distinguishes the different kinds of legs as follows :—1. Palpatorii; 2. Gressorii; 3. Remigantes; 4. Cursorii; 5. Textorii; 6. Carunculati.

The parts of the mouth consist of two movable pieces, or falees, in front of which is another piece (labium); on each side of the labium is a strong piece (maxilla), and from the outer side of each of the maxillae springs a palpus of four or five joints. The different forms and structure of these parts give good characters for the subordinate divisions of the Acaridea. The mouth parts in the species of Acaridea present greater variety than is to be found in any other order, no doubt owing to the greater variation in their mode of existence. In some instances the falees, maxillae, and labium form, by their union, a sort of tube or proboscis fitted for piercing, holding on to, and sucking the juices of their prey; when not so united, the falees are terminated variously by a didactyle claw, somewhat like the claw of crab, or by a movable fang (sometimes twofold) as in the true spiders (Araneidea), or they consist of “two long styles, which by moving backwards and forwards alternately, perforate the substance of their prey.”

The palpi of Acaridians are also variously formed, and, like the legs, have been minutely and well distinguished by Dugès, who (Z.c.) divides them into seven kinds.— 1. Rapaces, armed with hooks for seizing hold with. 2.

Anchorarii, found in aquatic species, and used for retaining their position by means of terminating points. 3. Fusiformes, without any claw on the last joint. 4. Filiformes, as their name implies, filiform, or not at all tumid. 5. Antenniformes, chiefly differing from the last in their greater length. 6. Valvaeformes, flattened, or excavated, or sheathed in form. 7. Adnati, or united throughout the greater part of their length to the labium, and always slightly developed.

The eyes in very many Acaridians are entirely wanting; When present they vary in number, being generally two, four, or six, and are placed on the cephalo-thorax; sometimes, as in the family Hydrachnides, they apparently consist of mere spots of pigment beneath the cuticle; 1 in some other cases there is but one eye, which is composed of a varying number of small facets.

Internal Structure. —The Organs of Digestion consist, in many species, of a short intestinal canal, which branches out into lateral caeca, “à sa partie stomachale,” and has an anal orifice on the lower side of the abdomen, more or less near to its posterior extremity (Walck., Ins. Apt., iii. 135). The researches of Dujardin {Ann. Sc. Fat. 1845, tom. iii. p. 14) show in two families (Hydrachnides and Trombidides) a curious modification of these organs. In this, the juices upon which these creatures exist are sucked in, apparently, into simple cavities in the substance of the body; these cavities are without walls of any kind, and from them the juices circulate through the body, and thus form its support.

The Organs of Respiration consist generally of tracheae, communicating outwardly with the air by means of minute orifices, “stigmata,” which, in the genus Oribates, are situated between the first and second pairs of legs. In one numerous family {Acarides) no special organs for breathing exist, respiration being apparently effected by the general surface of the body. Different genera exhibit these two modes of respiration in various forms of union. Μ. Dujardin {l.c., p. 17) speaks of tracheae, in the family Trombidides, having an external orifice at the base of the falces on their upper side,—the use of these tracheae being for expiration, while inspiration is performed through the general surface of the body and the plumose hairs attached to it, or, as in the family Hydrachnides, by “stomata,” i.e., apertures covered with very delicate membrane.

The Nervous System in Acarids is ganglionic, as in the rest of the Articulata; and, as we should expect from the simple form of the body (occasioned, as we have seen, by the almost complete fusion of the head and thorax in the abdomen) extremely simple. In the families Trombidides and Acarides, and probably in the rest also, the nervous apparatus consists of “one large globular ganglion, from which nervous filaments are given off, both before and behind.”

With regard to the Circulatory System in the Acaridea too little, apparently, is yet known to make it possible to speak certainly. It is highly improbable but that, in some of the higher groups, distinct organs exist, though such do not yet appear to have been discovered. The results hitherto are negative; no traces of circulatory organs have been found in such of the lower acarids as have been subjected to minute dissection, and hence the supposition 2 that the intestinal canal, by means of muscular movements and contractions, operates in the irregular propulsion of the vital fluid to various parts of the body.

The Reproductive System of the Acaridea is very simple. The external organs consist of an opening on the ventral surface, generally between the coxae of the hinder pair of legs. Acarids are both oviparous and ovo-viviparous; in the latter case the young are produced through a large orifice or vulva nearly one-third of the length of the body, and closed by two valves. Some are supposed to be hermaphrodite, but this, though true of the Pentastomides, is uncertain in respect to others of this order. Parthenogenesis, however, certainly exists in some species. The ova appear commonly to be produced in the substance of the general tissue of the body without the presence of auy ovarian apparatus with distinct walls; it is certain, however, that ovaries are present in some species—in the family Trombidides, for instance, in which a tubular double branched ovarium was discovered by Dujardin. Some of the Acaridea, as Tetranychus, produce silk, and spin webs, but the silk-secreting organs have yet to be discovered; neither do any external organs, such as spinnerets, appear yet to have been noticed. The development of Acaridians from the egg is a subject of great interest and importance, for which, see Claparède’s Studies on Mites {Studien αν Acariden), and Siebold in Kollikef ’ s Journ. Sc. Zool., 1868, part iv.

General Observations. —Acaridians are universally distributed; they are to be found under stones, dead leaves, or bark of trees, in the ground, in water, in unrefined sugar, upon dried meat, fruits, cheese, and putrid animal matters, upon all of which they feed. Some are parasitic, both externally and internally, in the flesh of different animals, living upon the juices of the creatures they infest. One species, Sarcoptes Scabiei, is the cause of tha disease called the “itch;” another is our troublesome “Harvest-bug.” Some are parasitic upon insects of different kinds; others are said to have been found in the brain and eyes of man. All are small, great numbers almost microscopic; the smaller kinds, particularly of the Acarides, are very difficult to preserve as cabinet objects, and from this, as well as from their minuteness, the order, generally, does not receive that attention to which, from their diversified forms and modes of life, Acaridians are certainly entitled.

From various considerations of structure, the Acaridea may be divided into ten families, each containing one or more genera. These families may shortly be characterised as follows :—

Fam. 1. Pentastomides.— Bodyannulate, vermiform, lancet-shaped; the segments of the cephalo-thorax continuous with the body, and furnished with four strong claws or rudimentary legs; this appears (Rolleston, Forms of Animal Life, p. 118) to be the larva or immature state, the adult form being destitute of limbs (which are replaced by four hooks—two on each side of the mouth), and reversing the ordinary progress of many acarids, from a fewer to a larger number of legs; organs of respiration and circulation, none (Huxley). On this abnormal·family, of which one genus and eighteen species have been described, see Cobbold’s Entozoa, pp. 393-402, and authorities there quoted. (See figs. 1, 2.)

1 Rymer Jones, An. King., 2d ed. p. 411.

s See Packard’s Guide to the Study of Insects, p. 627.

Fam. 2. Tanurides (rayais, long, ουρά, a tail).—The type of this family is Demodex folliculorum, Simon (fig. 3), a very curious parasite found in the follicles of the human nose—hence its specific name. It is long and slender; the abdomen drawn out into a wormlike tail; the fore part or cephalo-thorax has in the adult state four pairs of rudimentary legs, in the immature state three pairs. This is one of the lowest forms of acaridians, and presents in its adult state the immature vermiform appearance of the higher genus Typhlodromus (Packard, Z.c.)

Fam. 3. Tardigradides. — Body cylindrical, vermiform, but with no ∏ o . 3. _ Demodex folliculorum, distinct abdomen; it is furnished Simon; under side. a...a, rudi-throughout its whole length with mentary legs abdomen.. four pairs of rudimentary limbs, of which the fourth pair is quite at the posterior extremity; eyes, two; falees, style-like. These animals are microscopic in size and aquatic in habits; they are hermaphrodite, and are now generally held to be acarids of a very low grade (Packard, l.c., p. 66S). Several genera have been characterised. Fig. 4 represents Milnesium tardigradum, Schrank.

Fam. 4. Acarides.— We now come to the more typical forms of Acaridea.

The family Acarides have a soft, thin-skinned body, with the thoracic junction often visible; falces either scissor-like or stylifoπu; maxillae obsolete; legs of the two first pairs often widely distant from those of the hinder ones; in some lowly organised forms, “face-mites,” four legs only are found; perhaps these are the immature form of some other species (?); eyes, none. In this family are included the cheese, itch, and sugar mites, with numerous others parasitic on various animals. Some forms, as IIeteropus ventricosus (Newport), Dermaleichus, and Typhlodromus, particularly in the immature state, exhibit an evident link between the last two families and the higher acarids; on the agamic reproduction of a species of this family (Cheyletus) see R. Beck in Q. J. Microsc. Sc., April 1865; also Newman’s Zoologist, 2 ser., i. p. 236.

Fam. 5. Oribatides. — Body hard and horny; the thoracic junctions visible; form of the abdomen, round, globular, oval, quadrangular, or hemispherical; palpi, short; maxillae, large and toothed; eyes, almost obsolete; cephalo-thorax, generally with two wing-like projections and two or three cup-shaped pedicellated stigmata on the edge, leading to the respiratory tubes. The Oribatides in general live on vegetable matter, and several genera have been characterised. The immature forms of many species vary greatly from the adults, so that numbers have been described as distinct species. Seeon this family an elaborate paper by Μ. H. Nicolet, in the Arch, du Mus., t. vii. pp. 383-482, pls. 24-33.

Fam. 6. Gamasides.— Body, oval, flattened; epidermis, dense; falces, scissor-like; maxillae, free; legs, equal in size and of similar form; eyes, obsolete. There are several genera of this family parasitic on various animals.

Fam. 7. Ixodides.— Body, round, oval, or somewhat oblong, of a leathery consistency; palpi, short, three or four jointed; falces, saw-like, and, with the other parts of the mouth, joining in the formation of a beak for thrusting into and holding on to their prey. Eyes, often obsolete; legs weak. On the generation of Ixodes, see a paper by Prof. Gêné, communicated by A. Tulk to Ann. and Mag. N. H., No. 188, Sept. 1846, p. 160. When gorged with the juices of their victim the abdomen attains an enormous size, and appears almost to obliterate all the rest of the body. In this family are comprised the “ticks” (Ixodes), which are ofteq so tormenting to mankind, and domestic and other animals (figs. 5, 6). Among these ticks is included also the noted genus Argos, of which a species, A. reflexus (Latr.), has lately been found at Canterbury, England. Some of the largest known acarids are contained in this family.

Fam. 8. Hyarachnides, or water-mites.—Body, oval, or almost globular; palpi, short; legs, ciliated for the purpose of swimming; eyes, two. These acarids are found in salt as well as in fresh water. Some are parasitic, when immature, on water-bugs and water-beetles; others, through life, on the gills of the fresh-water mussel.

Fam. 9. Trombidides.— Body, stout, round, or oval, and often somewhat oblong; frequently broader before than behind; sometimes clothed densely with a kind of pubescence. The two hinder pairs of legs far removed from the two fore pairs. Eyes, two. The colour of the species of this family is generally of a bright red, scarlet, or yellowish. Among them is the red mite, Tetranychus telarius (Linn.), popularly called the “red-spider,” which infesta hothouses.

Fam. 10. Bdellides.— Body, oblong-oval, showing the junctions of caput, thorax, and abdomen; palpi, long; eyes, two to six, sometimes obsolete; legs, long and strong; parts of the mouth forming a tapering pointed beak of greater or less length, and looking like a prolongation of the caput. The Bdellides live in damp places, undèr moss, &c., and on the floors of caverns.

The above characters of the Acaridian Families are abridged chiefly from A. S. Packard’s Guide to the Study of Insects. Besides Claparède’s Studien an Acariden, and Nicolet’s Mémoire on Oribatides, and other works above noted, may be mentioned Dr C. Heller on the anatomy of Argas persicus, Sitzιιngsb. d. K. Akad. d. IV. Math. Naturw. Cl. Bd. xxx. No. 13, 1858, pp. 297-326, Taf. i.-iv., Charles Robin's Mémoire zoologique et anatomique sur diverses espèces d'Acariens de la Famille des Sarcoptes, 1860, with 8 plates; also by same author, “Mémoire sur les Sarcoptes avicoles, et sur les metamorphoses des Acariens,” Comptes Rendus, tom. lxvi. pp. 776- 786; H. A. Pagenstecker, Beiträge zur Anatomie der Milben, Heft 1, “Trombidium,” 2 Taf. 32 pp., Leipsic, W. Engelman, 1860; P. J. van Beneden, “Recherches sur l’histoire naturelle et la développement de l’Atax Ypsilophorus (Hydrachna concharum)," Nouv. Mém. de l'Acad, de Belge., tom. xxiv. 1850 (24 pp. ed. 1. pl.) Of the older works on Acaridea maybe mentioned that of Hermann, Mémoire Apterologique, in fol., Strasbourg, 1804; andP. Gervais, in Walcke-naer’s Ins. Apt., tom. iii. pp. 132-288, pls. 31-36 and 38, 1844; Doyère, “Mémoire sur les Tardigrades,” Ann. Sc. Nat., 2 ser. “Zool.,” tom. xiv. 1840, pp. 269-361; Suite, Ibid., torn. xvii. 1842, pp. 193-205, and tom. xviii. 1842, pp. 5-35, with 8 plates; P. J. van Beneden, “Recherches sur l’organization et la développement des Linguatulos (Pcntastoma, Rud.) suivies,” &c., 39 pp. with 1 pl., in Nouv. Mém. de l'Acad, de Belge, tom. xxiii. 1849.

Order IL— Pycnogonidea.

The creatures of this order form a small group which it appears now necessary to receive among the Arachnida, though their true position has been hitherto (and to some extent still is) a matter of much difference of opinion among naturalists. They seem to connect the more typical Arachnida with the Crustacea, and also to form a passage from the Acaridea to the Phalangidea. It appears, however, when their peculiar structure, both external and internal, is considered, impossible to include them within either of those orders; it is therefore proposed here to constitute them a separate order between the acarids and phalangids. The characters of the order are—

External Structure.— Body, linear, composed of four segments; caput, tubular, in form of a beak or proboscis, and either simple, or ending with palpi and mouth organs; abdomen, rudimentary; legs, eight (each thoracic segment bearing a pair), very long, and consisting of eight to nine joints, terminating with a claw or claws. In the immature (so-called larval) state the legs are four only in number. The females have a supernumerary pair between those of the first pair, used for carrying the ova. Palpi, when present, filiform, and composed of five to nine joints terminating with a claw. Eyes, four.

With regard to their internal structure, the Pycnogonidea have a dorsal vessel (circulatory apparatus) divided into chambers, a stomach sending forth caecal prolongations into the legs and palpi, an abdominal intestine with dilated cloaca, and a nervous system, consisting of a cephalic and opththalmic ganglia, closely united together and joined by the cesophagian fillet to the abdominal ganglia, which are four in number, of large size, sessile, and emitting from their lateral extremities nerves into the legs (Cuvier’s Règn. An., edition cited post, pl. 22), but no organs of respiration (Huxley, l.c., and Cuvier’s Regn. An., l.c. )

This order contains but one family, Pycnogonides, divided into several genera—Pycnogonunι, Phoxichilus, Nymphon, and Ammo-thsi. Some of the species ere parasitic on cetaceous animals, others are found secreted among seaweed along the sea-shore, and feed on small marine animals. Some are British, and others exotic.

The genera may be thus shortly characterised.

Genus Pycnogonum (Brunnich).—Body short and thick; legs, short, strong; without either falces or palpi. The species of this genus are parasitic on the cetacea. Figs. 7, 8, P. littorale (Müller).

Genus Phoxichilus (Latr.)—Body narrow; legs of great length; falces present, but no palpi.

Genus Nymphon (Fabr.)-Besembles Phoxichilus in the narrow body and long legs, which are also slender, as well as in having falces; but in the present genus there are also two palpi, each of five joints. Fig. 9, Nymphon coccineum (Johnston).

Genus Ammothca (Leach).— Body short and lather broad; legs long; beak of great size and length; much longer than the falces, which are short. Palj i 9-jointed, the third joint much the longest; terminal tarsal claws double, and of unequal size. Supernumerary legs 9- jointed, and inserted under the first pair of legs behind the beak.

The latest authority in regard to their systematic position, i.c., whether Crustacean or Arachnidan, is Dr Anton Dohm, who says in a memoir, “Ueber Entwicklung und Bau der Pycnogoniden” (contained in a publication, entitled Untersuchungen über Pau und Entwicklung der Arthropoden, Leipsic, Engleman, 1870): “Die Pycnogoniden sind weder Arachnideu noch Crustaceen.” Dr Dohm enters fully into the development and structure of Pycnogonum littorale, and of a species of another genus formed out of Phoxichilus, Achclia lccvis. The present writer has not, however, had an opportunity of studying this memoir.

Order Z7Z. —Phalangidea.

The Phalangidea present a very well defined and compact group, though the transition, in one plane, from the Acaridea, through the families Cyphophthalmides and Trogulides, is tolerably apparent, while in another plane they show evident affinity to the Pycnogonides. The following are more detailed characters of the order :—

External Structure. —The body is of a more or less round, oval, or oblong, and sometimes quadrangular form; the integument is either hard and horny, or coriaceous, and generally destitute of hairs, but often tuberculous and armed with spines.

Thé cephalo-thorax and abdomen are united throughout their whole breadth, the junction frequently shown by a slight constriction, but always visible from a strongly-marked groove or ridge; the upper side of the cephalothorax, and sometimes of the abdomen, is frequently furnished with spines, sharp teeth, or tubercles. The abdomen is articulate, or segmented in a modified form, from several more or less strongly developed transverse foldings in the epidermis.

The mouth organs are rather complex (fig. 11), consisting of three pairs of maxillae, above which is a tongue (languette) ; and below the maxillae is a membranous lip (labium). From the first pair of these maxillae there issue two five-jointed palpi, the intermediate joints of which often exhibit processes or branches, the last or digital joints ending with a claw. The other two pairs of maxillae support the basal joints of the two first pairs of legs. The presence of these supernumerary, or crural, maxillae strongly supports the idea long since advanced by Savigny and others, that the palpi are but modified legs (see, however, note 1, p. 272 supra); the same idea being also raised in regard to the Thcly-phonidea and Solpugidea by the use as palpi of the first pair of legs, which are in fact completely palpifoπn, and differ markedly from the rest in their structure. Abo^e these parts, directly in front of the upper extremity of the cephalo-thorax, are two falces, each of which consists of two, or (in Cyphophthalmides, G. Joseph) three joints; the second joint terminates with a didactyle claw or pair of pincers, formed by a movable claw acting in opposition to a fixed one.

The falces vary greatly in their size and development. The terminal joint is sometimes articulated to the basal one at the extremity of its longer axis or at its end; at other times it is attached by its shorter axis, or more or less near the middle. In some species they are furnished with processes or horny prolongations, differing in size and form in different species; this is, however, only a modification of the last mentioned mode of articulation.

The legs are, in most species, very long and slender; in some groups they are, however, shorter and stronger, while in others they are of extreme length and tenuity. They are eight in number; the seven normal joints, of which each is composed, may be more properly described as consisting of five invariable and two variable ones; the sixth (or metatarsus) being divided into several immovable divisions, and the seventh (or tarsus) subdivided into a greater or less number of minute movable articulations, the terminal one furnished with one or two fine claws. The legs are often armed (some, at least, of their joints) with strong spines and spiny processes; this is particularly the case in the family Gonylep tides. The first joint (coxa) of each leg is immovable, being fixed to the side and under part of the cephalo-thorax. Between the fixed (or basal) joints of the legs is an oblong, or at times somewhat obtusely triangular, sternal plate, divided at its base fro⅛ι the abdomen by a transverse groove; the anterior extremity is free, and beneath it is concealed (according to the sex) the penis of the male, or the ovipositor of the female; in some species of Phalangides these organs are of great length and varied in form; this sternal plate forms the lower side of the cephalo-thorax. The eyes, two or eight in number, are generally of large size, and situated on the sides of a common eminence on the upper side of the cephalo-thorax; this eminence is often armed with spines and tubercles.

Internal Structure.— Muscular System.— Every one who has seen the mode in which the Phalangides run would naturally suppose that the muscles required to keep the body raised and balanced between their long slender legs in rapid course must be exceedingly strong; and this is found to be the case. The muscles are of large size, consisting of numerous strong “fasciculi,” which arise from the interior of the basal joints (coxae) of the legs, and, almost entirely filling up their hollows, pass on into the next joint (trochanter), and so on to the end of the second part of the tibiae; thence two long delicate tendons, continuing forwards, traverse the whole length of the tarsal joints, running along their under surface. The muscles by which the falces and palpi are worked consist of an elevator and a, somewhat larger, depressor for each. Other muscles and muscular fibres connected with other parts and organs are minutely described by A. Tulk, whose descriptions, however, cannot be usefully abridged, and are too extensive and detailed for our present space.

Organs of Digestion.— These consist of a simple longitudinal pouch forming the stomach or main intestinal canal, contracted at each end, enlarged in the middle, and giving off on all sides numerous lateral pouches or caeca of different sizes, to the number, in Phalangium opilio (Latr.), of thirty. These are minutely detailed by Tulk, who divides them into—(1), those on the dorsal surface of the main canal; (2), those on its ventral surface; (3), those on its sides. The pharyngeal tube and oesophageal canal are modified so as to be qualified not only for the passage of simple fluids, but also for solid substances; these first, ∣however, having undergone a process of quasi-mastication by means of the external parts of the mouth. At the opposite end of the alimentary canal a simple, short intestine connects it with the anus, the external aperture of which is situated at the hinder extremity of the abdomen. With regard to the office of the lateral caeca, an examination of their contents has led to the suggestion that they secrete a peculiar granular substance, which is thence discharged into the stomach, and “agglutinates the particles of food together,” covering them with a membranous integument which serves to protect the delicate coats of the intestine from laceration by the sharp and spiny nature of their food-contents (Tulk, l.c. p. 248). Biliary tubes have been described by Treviranus; but it seems probable that the anterioι pair of these, at least, are tracheae connected with the stigmata or each side of the fore margin of the cephalo-thorax. These stigmata were mistaken by Tulk for eyes {l.c. p. 156).

The Organs of Respiration are tracheal. The stigmata in Phalan∙ gium (and Gonyleptes ?) are four in number,—two beneath the fore part of the abdomen, situated one at the base of each of the posterioι legs, but usually concealed by the coxal joints, and one on each side of the fore margin of the cephalo-thorax; each of the former ρaiι opens into a large obliquely longitudinal tracheal trunk; these twc trunks give off various smaller branches and tubes, which convej the air to all parts of the body. With two of these tubes, probably, the cephalic stigmata are connected.

The Organs of Circulation are very simple, consisting, in Phalangium, of an elongated dorsal vessel acting as a heart, lying in a groove upon the upper surface of the alimentary canal, and divided into three chambers. Ramifications from this vessel serve to carry the vital fluid to every portion of the body /Tulk). From researches since made by Μ. Blanchard, it appears that this fluid is recollected from the general circulation into two large lateral vessels (vascular sinuses), from which it is returned by other channels to the dorsal vessel, or heart itself. The structure of the heart consists oi a series of transverse, curved, and muscular bands, leaving between them light and membranous intervals (Tulk).

The Nervous System of phalangids is very similar in its type to that of some other arachnids. Two large ganglia (cephalic and thoracic) occupy the cephalo-thorax, and from these nerves issue to the various parts, some of them leaving ganglionic enlargements in their course, whence again finer nerves distribute themselves to the adjacent structures. Tulk mentions a strildng peculiarity connected with the nervous system of phalangids, which is a power possessed by them to move the nervous centres backwards or forwards at will; this is effected by means of several large transversely striated muscular fasciculi radiating from the sides of the thoracic ganglion, to which they are attached by short tendons (Tulk, l.c. 326).

The Organs of Generation in the Phalangidea (which are oviparous), are different from all other arachnids in the large external parts connected with them. In the female, the internal parts consist of an ovisac and ovarium (Tulk); whence, by means of the oviduct, the ova are conducted into the ovipositor. This is a long membranous tube; the first or basal part of it is surrounded by annuli or rings of hairs or bristles; towards the extremity it is scaly, and also furnished with some hairs, and the extreme point has two small lateral tufts of hairs. The ovipositor is protruded, at the will of the animal, from the vulva, which is situated at the fore margin of the sternal plate, or else it is, when at rest, withdrawn into its sheath, leaving no outward trace of it visible. In the male, the seminal vessels consist of a cluster of “slightly tortuous caecal tubes,” whence the spermatic fluid is passed by a duct into a penis of enormous length compared to the size of the animal (fig. 12, d, e, f). This organ is a slender curved tube, furnished at its extremity with a recurved hook, and contained in a sheath; both the sheath and penis when at rest lie in a longitudinal direction beneath the ventral surface, of the thorax, but can be protruded at will from the external aperture, which is similar, and similarly situated, to that of the female. The form of the penis varies in different species, as also does the ovipositor of the female. The organs of generation, both male and female, of Phalangium opilio, are detailed a great length by Tulk, l.c. Both the penis and ovipositor may be made to protrude by ,’a slight lateral pressure beneath the fore margin of the sternal plate.

General Observations. —The Phalangidea have been found in all parts of the world, but though often very numerous in individuals, the number of species as yet discovered is comparatively small. In the British Islands, where about sixteen species have been observed, they are popularly known by the name of “Harvest-men,” probably because most numerous at the time of harvest. They run with great rapidity over and among grass and low herbage, and many live among the leaves and mossy covering of trees, among moss on the ground, heath, and stems of herbage; also under stones, and among rubbish and debris. Their prey is small insects, the young of the true spiders, and some species of Acaridea. The small size of the body, compared with the inordinate length of the legs, in some genera is exceedingly striking. In an undescribed species of Leiobunus, from the Brazils, the length of the body is but a line and a half, while that of the longest legs exceeds fifty lines; being in the proportion of about 1 to 32. Phalangids part easily with their legs, or with portions of them; and when detached these legs retain the power of motion for a considerable time, due probably to sustained nervous energy. The order may be divided into about four well-marked families.

Fam. I. Cyphophthalmides.— Characterised by an oval, flattened body, short legs, with undivided tarsi; falces projecting far in front of the fore part of the caput, and three-jointed (Joseph). Eyes on pedicles, one on each side of the cephalo-thorax near the lateral margin. One genus only, Cyphophthafinus (Joseph), and two species, C. duricorius (Joseph), and C. corsicus (Simon), have as yet been discovered, both of very small size, and both South European. They have an exceedingly acaridian appearance, and seem evidently to connect the acarids with the more typical Phalangidea. See G. Joseph (Berl. Ent. Zcitschr. 1868, pp. 241-250 and 269-272), who speaks of but two tracheal stigmata; probably the thoracic stigmata were overlooked. The form of the maxillae appears to be peculiar.

Fam. II. Trogulides.— Somewhat similar in general appearance to the former family, but differing in the parts of the mouth being concealed beneath a kind of hood, which projects beyond the fore margin of the cephalo-thorax; and in the eyes, which are placed, well separated, in a transverse line at the constriction, where the hood joins the caput. Two genera, Cryptostemma (Guerin) and Trogulus (Walck.), have been characterised; of the former one species only is yet known. C. Westermanni (Guer.), Guinea. Of the latter genus the species are few, and little appears to be known of their habits or economy; one only, of small size, Trogulus Cambridgii (Westwood), has been found in England (at Blcxworth, among moss, by the Rev. O. P. Cambridge), remarkable from the dense clothing of short squamose hairs on the body, and hooked spine-like bristly hairs on the legs.

Fam. III. Phalangides (figs. 10, 11).—Characterised by their small.

round, oblong, or oval body; exceedingly long, slender legs, with multi-articulate tarsi; eyes close together, one on each side of a tuberculous eminence on the vertex of the cephalo-thorax (fig. 12, α); the eminence, as well as other parts of the body, often armed with spines. Falces (fig. 13) often of great size and length, the terminal joint articulated sometimes at its end, sometimes further on. Several genera of this family have been characterised, and numerous species recorded, mostly European, but our space will not permit of further details, which may be found in the work of Hermann before noted, under Acaridea; also in those of Latreille, Sur T Histoire des Insectes connus sous le nom de Faucheurs (Phalangium) (pub. 1802), and

Herbst; in Natursystem der ungefliigelten Insekten, 1798- 99; P. Gervais, in Walck. Ins. Apt.pvoX. iii. p. 94; and Koch, in Die Arachni-den, 1831-1848; and in numerous isolated papers by various later authors. Most of the anatomical details known of the order Phalangidea have been obtained from species of this family.

Fam. IV. Gonyleptides.— This differs from the last in the generallymore or less quadrangular form, or roughly diamond shape; the cephalo-thorax is proportionally larger, often appearing almost entirely to overwhelm the abdomen; it is also more spinous and tuberculous; the palpi are longer, some jointsoften of great strength and length, and armed .with strong spines, sometimes assuming, with the strong terminal movable claw, a raptorial appearance. The legs are shorter and stronger, and those of the hinder pair are usually armed with spiny processes, tubercles, and spines; the coxal joints being often inordinately developed, reaching to the extremity of the abdomen, to which, as well as to the cephalo-thorax, they are immovably attached. The tarsi are not multi-articulate. The species are tolerably numerous, and all exotic. Several genera have been characterised, on the species of the chief and typical one of which, Gony∙ leptes (Kirby), a Synonymic List, with descriptions of some new species, has been published by Mr A. G. Butler, in Ann. and Mag. N. H., Feb. 1873, pp. 112, 117, pl. 3., continued in Jour. Linn. Soc. 1874, vol. xii. pp. 151-155, pl. 8. Some of the works quoted on Phalangides also treat of this family. H. C. Wood, jun., considers the order generally in Trans. Amer. Phil. Soc., U.S., vol. xiiι. pp. 435-442, pl, 24.

Order IV.— Solγugidea∙

This order constitutes a small but very distinct and remarkable group of tropical and semi-tropical Arachnids. At first sight they remind us a good deal of the true spiders (Araneidea), but their position, when we examine their structural details, seems to be more naturally assigned between the Phalangidea and the next order (Scorpionidea) (figs. 14,15).

External Characters. —The body is elongated and clothed with hairs; it is divided, as in other Arachnids, into two main portions (cephalo-thorax and abdomen), but each of these portions is composed of several segments or articulations. The caput forms the first segment of the cephalo-thorax; and this is followed by three others closely united to each other, and of a somewhat quadrangular form. Close behind each coxal joint of the legs of the second pair is a small transverse slit or stigma leading to tracheae.

The eyes are two in number, and seated on a tuberculiform eminence on the fore part of the caput; this eminence is furnished with two long slender spines, placed in a transverse line between the eyes, and projecting forwards.

The legs, articulated by a fixed joint to the lower surface of the thoracic segments, are long and strong, furnished with hairs (some of which are remarkably long), bristles, and spines, varying in length and strength. The legs of the first pair are palpiform and not used in running, probably having the sole office of feelers. The number of joints of those of the first and second pairs is seven, while those of the third and fourth pairs have eight, an extra joint being inserted between the basal and next adjoining joints; the tarsi of the first pair are simple, or undivided, and terminate with two small curved claws, while those of the other three pairs are often divided into two, three, or more articulations, besides a small terminal or heel joint, from which spring two long curved finger-like claws, each ending with a curved (apparently movable) nail or talon. The number, however, of the tarsal joints appears to differ in some species from others, and even in the different legs of the same species. The legs of the second, third, and fourth pairs belong to the three thoracic segments respectively, while those of the first pair are closely united (and even soldered) by their basal joints to the basal joints of the palpi beneath the caput, thus furnishing an additional reason for supposing them to be more of a palpal than of a crural nature; between the bases of the first pair is a small triangular piece (with its apex directed forwards), unnoticed by authors hitherto (?) and which may be regarded as a rudimentary sternal lip (labium); on the under sides of the three basal joints of each of the fourth pair of legs is a longitudinal row of five curious scale-like or lamelliform appendages, of a subtriangular or somewhat fish-tail form, each articulated to a separate foot-stalk, which is again articulated to the surface of the leg joint; beginning from the basal joint the form of the last two of these appendages differs a little from that of the rest. That these remarkable portions of structure have some special office is scarcely to be doubted, but as yet their part in the animal economy has not even been conjectured. They appear to differ slightly in structure in different genera.

Articulated immediately below the fore-margin of the caput are two enormous, massive falces, each consisting of a single joint, and ending with a didactyle claw or pair of toothed jaws, the upper fixed, the lower movable, and articulated horizontally with a vertical movement, closing upon each other like scissors or shears; these falces are projected in a line almost parallel with the caput, and are generally equal in length to the whole of the cephalo-thorax. From the fore part of the upper side of each of the falces are often seen one or two curious elongate styliform appendages varying in size and form; their use, if any, which may be doubted, is unknown; they are probably distinctive of sex, and appear to be characteristic of species. Underneath the caput, and forming the basal joints of two long strong five-jointed palpi, are the maxillae; these are strong, cylindrical, and have a more or less strong blunt-pointed apophysis at the extremity on the inner side. Like similar parts in other Arachnids, these maxillae, in conjunction with the affixed basal joints of the first pair of legs, form the lower boundaries of the mouth, the labium (mentioned above) being apparently too rudimentary to subserve any practical purpose. The palpi are furnished with hairs, spines, and bristles similar to the legs, and the last (digital) joint consists of a kind of capsule containing a peculiar organ, said to be protruded only when the animal is in a state of irritation, the use of which does not appear to be known; doubtless it has some special function beyond that of a mere palpus, and the analogy of the use of the palpi in the males of the Araneidea would lead us to suspect a similar use in the present instance, i.e., as connected in some way with the process of generation. Between and within the maxillae is a portion of the mouth organs, composed of several parts of a peculiar shape, and furnished with two slender feather-like appendages; this is called by Walckenaer the lip (Al·re); but its place and office is undoubtedly more that of the tongue (languette), though probably in the rudimentary state of the true labium it partly performs the duty of a sternal lip. Dugès and 31. Edwards in Cuvier’s Règne Animal (Arachnides, p. 83), speak of the “labre,” but it is evident from their description that a portion of the languette is alluded to, not the part mentioned above as representing the labium. The abdomen is oblong, oval, or somewhat elliptic in its form, about equally convex above and below, and composed of nine or ten articulations, which decrease in breadth from the fore to the hinder extremity; it is closely united to the cephalothorax throughout its entire breadth. The external orifice leading to the organs of generation is situated at the posterior margin of the first articulation, and besides the two stigmata before alluded to, behind the basal joints of the second pair of legs, there are two other stigmatic openings at the hinder margin of each of the second and third articulations of the abdomen; these stigmata are protected by a kind of comb-like fringe, and the anal orifice consists of a long vertical slit situated at the extremity of the terminal articulation.

Internal Structure. —The Muscular System, of Solpu-gids appears to be very similar to that of other Arachnids; it has been fully displayed by Dr Μ. Kittary in the work quoted in note, of the present page.

The Respiratory System is tracheal and complicated. Five (according to Dr Kittary) openings at the hinder margins of the second, third, and fourth sub-abdominal articulations, lead to the abdominal tracheae; these consist of three longitudinal parallel tubes, into the outer one of which the short branches from the external openings lead, and with these are connected various other branches supplying air to the different parts of the body. The abdominal tracheae also lead into those of the cephalo-thorax, which have their outer openings (two in number) behind the basal joints of the second pair of legs. The thoracic tracheae send branches into the legs, palpi, and falces.

There is probably some variation in different species in the details of their respiratory organs. Galeodes Araneoides, for instance, does not appear to have the fifth outward opening in the abdomen (fig. 15).

The Circulatory System consists of an elongated dorsal vessel or heart, running from the middle of the cephalothorax backwards through the connection between the thorax and abdomen, but does not reach the hinder extremity of the latter. The thoracic portion is of an oval form, but it contracts in passing into the abdomen, enlarging again gradually as it runs backwards. Dr Kittary does not appear to have traced the various vessels which, no doubt, exist to convey the vital fluid from the heart to the different parts of the body.

The Organs of Digestion consist of an elongated stomach in the cephalo-thorax, with lateral caeca; this stomach is continued backwards into the abdomen in the form of a long single intestinal canal, leading into a cloaca at its posterior extremity. A kind of branching network of minute vessels secrete urine, and convey it from the whole abdominal mass by several main branches into the hinder part of the intestinal canal. Beneath the stomach is an organ described as probably the liver, and another answering to the pancreas.

The Nervous System is not particularly complicated, but bears great resemblance to that of other Arachnids, especially of the Araneidea. It consists of one large principal ganglion, or united pair of ganglia, from which branch nerves are sent off in all directions to the different parts and extremities of the body; that which runs to the hinder extremity of the abdomen has an enlargement or kind of ganglion in its course.

The Organs of Generation are highly developed in the female, consisting of ovanes, and an oviduct leading to the external orifice. The male organs do not appear to be known. The Solpugidea are probably oviparous.

The order Solpugidea comprises a single family, Galeodides, divided into five genera, characterised principally according to the number of the subdivisions of the tarsal joints of the second, third, and fourth pairs of legs :—1. lthax (Hermann), the tarsi all one-jointed. 2. Acllopus (Koch), tarsi two-jointed; those of the hinder pair destitute of claws (Koch). 3. Galeodes (Olivier), tarsi of the second and third pairs two-jointed, and of the fourth pair three-jointed. 4. Solpuga, tarsi of the second and third pairs four-jointed, and of the fourth pair seven-jointed. 5. Gluvia (Koch), all the tarsi undivided, i.e., consisting of a single long thin joint.

Fifty-two species (of all the genera) have been described. See a recent paper, List of the Species of Galeodidcs, by A. G. Butler; also the older work of Koch, Die Arachniden. All the species, though varying considerably in size, are remarkably similar in general form and appearance, and nearly all are of sombre colouring.

General Remarks. —The Solpugidea are nocturnal in their habits, living by day secreted under stones, among debris and rubbish, and in old ruined walls and buildings, in dry sandy places; from such retreats they come forth at night, and run with great swiftness. A recent traveller in Palestine relates, that when living in tents on the plains of the Jordan, near Jericho, each night, as nearly as possible between half-past nine and ten o’clock, several Solpugids entered the tent-door, running and racing with great speed over everything—tables, chairs, and beds—just like mad creatures, but apparently with no definite object, perhaps only attracted by the lights burning in the tent. When disturbed in their diurnal hiding-places they showed fight and were extremely pugnacious; but their being venomous is doubtful, though the Arabs seemed to dread them quite as much as they dreaded the true scorpions, which were also numerous under the large stones lying about. Some interesting details of the voracity and habits in confinement of a species of Galeodes, are given by Captain T. Hutton, Ann. and Mag. N.II., 1843, vol. xii. p. 81. Like the Phalang-idea, it swallowed the solid parts of insects, and even of a lizard five inches long. Captain H. assumes, as one use at all events, of the palpal organ mentioned above, that it is “a retractile sucker,” to enable it to ascend smooth surfaces. This, however, is veιy questionable.

Order V.— Scorpionidea.

In spite of differences in their internal anatomy, which appear to ally the Pseudo-Scorpionides more to the spiders than to the true scorpions, some leading features of external structure seem to stamp them at a glance as most nearly related to the latter. The impression inevitably created on a comparison of the true and false scorpions is that the latter are little scorpions without tails. Including them, therefore, here in the same ordinal group as the true scorpions, we may shortly characterise the order as follows: —Body elongated-oval; cephalo-thorax of one undivided piece, hard, homy, and often tuberculated or granulose, while traces of thoracic segments soldered together are generally more or less perceptible. Abdomen united to the cephalothorax throughout its entire breadth, and composed of several segments formed by articulated transverse coriaceous plates on the upper and under sides, united by two lateral cartilaginous membranes. Falces didactyle; palpi terminating with a didactyle claw or pair of pincers; the coxal joints of the legs, fixed to the lower side of the thoracic segments, form a kind of sternum; the sternal plate, properly so-called, being either wanting or very rudimentary. Eyes various in number, two to twelve. So far the true and false scorpions run together, but when compared more closely, differences, especially of internal structure, appear, which necessitate their subdivision into two groups or sub-orders. Menge and others, on account of these differences, separate the two groups more widely still; but one chief ground of this wider separation, the respiratory system, being in one tracheal, in the other (so-called) pulmonary, seems scarcely sufficiently well established to warrant it. Not that there is not a wide difference in their respective respiratory systems, but that the whole question of the respiration of Arachnids is hardly so settled as to justify any broad lines of classification being based upon it. In some groups of the first order, Acaridea, and also in the second (Pycnogonidea), no traces have been yet found of a distinct respiratory system, though perhaps this arises from the minuteness of the creatures themselves and the extreme delicacy of the membranous walls of the air-vessels. This latter especially, as has been lately observed in regard to some obscure Myriapodous insects,— Peripatus (H. N. Moseley, “Challenger” Expedition, 1874, Ann. and. Mag. N. H., 4 ser. vol. xiv. p. 225),—would make it almost impossible, by any means, to discover these tracheal tubes, when once the air had been expressed from them. Then, again, the so-called pulmonary organs of the true scorpions appear to be, simply, modified tracheae, entirely destitute of that which specially stamps the true lung, that is, the presence of blood-vessels bringing the vital fluid together, and carrying it through the respiratory organs for aeration. The Araneidea, moreover, have both the tracheal and so-called pulmonary systems combined; and also in this (more extensively worked than any other) order—Araneidea—the researches lately published on their organs of respiration by Philipp Bertkau (Arch. f. Nat., xxxviii. 1872, Heft. 2, pp. 208-233, pl. 7), show how much has yet to be learnt concerning this part of their internal structure. Considering, therefore, that the difference between the respiratory systems of the true and false scorpions should not separate them from the same ordinal group, these with other differences yet appear to necessitate a division within the order. We propose, therefore, to distinguish them under two sub-orders :—1. Pseudo-Scor-piones; 2. Scorpiones.

Sub-Order I.— Pseudo-Scorpiones.

These are distinguished from the Scorpiones chiefly by the absence of a tail and by their mode of respiration (figs. 16, 17, 18). The body is of an oblong-oval form; the cephalothorax is coriaceous; the abdomen sessile and, generally, composed above of eleven, underneath of ten segmental rings or articulations, usually covered above and below with a double longitudinal series of transverse corneous plates, united laterally by a membrane, the folds of which correspond to the transverse plates. In the second sub-abdominal segmental plate, on each side of the median line, there is (in some species) a small spiracular opening, and in the lateral connecting membrane of the third segment, opposite to the end of the third sub-abdominal plate, on either side, is another similar opening. These four stigmata are the external apertures to the tracheary system (fig. 18); behind and between the two first mentioned stigmata is a spinning organ, furnished with minute tubes for the emission of the silken threads; and close to this spinner, at the fore margin of the first abdominal segment, is the genital aperture.

The legs are closely affixed by the coxal joints to the lower side of the cephalo-thorax, and sit closely to each other, having a very small longitudinal space between them analogous to a sternal plate, of which, however, there is not even a rudimentary one, properly so-called. The number of joints in the legs is seven (Menge), but there appears to be a variation in this respect in some species. Each tarsus ends with two curved finger-like claws terminating with a short nail, and beneath them is another claw, modified at its extremity, gradually enlarging into a kind of conical form, probably acting as a sucker for the purpose of adhesion to smooth objects (fig. 18, <Z). The tarsal claws spring from a small heel or claw-joint.

The palpi are five-jointed, long and strong, terminating with a digital joint of large size, more or less bulbous at its base, and drawn out at its extremity into a jaw-like claw, furnished with hairs and bristles, and generally serrated along its inner edge. Against this claw another, articulated to the extremity of the bulbous portion, acts in opposition like tho pincers of a crab. Supporting the palpi on either side are the maxillae, forming the lower side of the mouth, the upper side being formed by two didactyle falcee; besides the movable jaw of the falces, there are connected with them some denticulate spines, or other spiny processes and bristles. Within the mouth is a tongue, which also serves as a sternal labium, and differs in its form in different species. The eyes, two or four in number, are situated on each side of the fore part of the cephalo-thorax, but there are none in the medial line. In some instances eyes are wanting altogether.

With regard to internal structure, the Pseudo-Scorpi-ones are very similar in their muscular system, to the spiders (Araneidea) (Menge). The digestive apparatus is simple; a large stomachal pouch contracted a little in the middle lies in the thoracic cavity, and from it the alimentary canal runs through to the hinder extremity of the abdomen, with a double crook in the course of its passage; this canal is imbedded on all sides in a mass of substance serving the function of a liver. The external spinning organs have already been mentioned; the internal apparatus resembles that of spiders, consisting of a number of small elongated pear-shaped sacs, communicating outwardly with the spinning tubes.

Nothing certain appears to have been discovered in regard to the circulatory system of the pseudo-scorpiones, except that a simple vessel runs along beneath the middle of the abdominal ridge; the vital fluid being found free among all the other organs of the body, so that the air is conveyed to the blood by numerous air-tubes, and not the blood to the air.

The tracheal character of the respiratory system has been just mentioned. The spiracular openings vary in number in different species, two or four. From the two hindermost of the abdominal apertures, when four are present, there issue more or less numerous thread-like tubes, which convey the air to the different parts of the abdomen. From each of the two foremost stigmata a main tube runs obliquely through the thoracic region, and from this tube finer ones issue to the rest of the cephalo-thorax and its adjacent parts—legs, palpi, and falces. When two spiracular openings only are present a large tube runs from each forwards into the thorax, and finer ones backwards into the abdominal parts.

The reproductive organs are simple. The external parts in both sexes are situated in the second (1) segment beneath the fore part of the abdomen, and consist of two small oval openings close together. Into each of these there opens in the male a curved horn-like sac, with a lateral direction, as well as a smaller longitudinal duct, the latter leading from a common seminal receptacle. In the female a two-branched oviduct leads from the ovaτia into the external apertures; the mode of reproduction is oviparous, and the eggs are carried by the female beneath the fore part of the abdomen, somewhat like those of certain of the Araneidea.

General Observations. —The Pseudo-Scorpiones are all of very small size; they do not appear to form more than one family group, Pseudo-Scorpionides, of which several genera and numerous species have been described by various authors. They are widely distributed, being found in tropical as well as in temperate climates. Europe possesses many species, and even England has several— these being the sole representatives of the Scorpionidea in this more northern latitude. Their habitat is under stones, beneath the decaying bark of trees, on the damp soil, among moss and herbage; some are found amongst old papers in houses, and in herbaria, and others are said to be parasitic on the common house-fly. For more minute details of structure and other particulars, see A. Menge, Ueber die Scheerespinnen, Chemetidce, who separates them from the scorpions under the above name, as a family group, more nearly allied by their internal structure to the true spiders than to the former. Menge gives also a list of works on this sub-order. A paper lately published by Dr Ludwig Koch, at Nuremberg, 1873, pp. 68, describes and gives analytical tables of all the European genera and species at present known.

Sub-Order IT.— Scorpionidea.

Between the solpugids and the scorpions (figs. 19, 20) the last group (Pseudo-Scorpiones) gives us an evident connecting link.

In the present sub-order, Scorpionidea, or true scorpi ons, the External Structure consists of a more or less elongated-oval body, covered with a coriaceous, or hard and horny integument. The cephalo-thorax is tuberculate or granulose, and marked with various seams, or grooves, and ridges, no doubt indicating the union of the caput and thoracic segments. One longitudinal, and, in general, strongly marked groove always divides the caput longitudinally, dividing also the tubercle on which the central pair of eyes is placed. This groove possibly represents the union of the two segments of a kind of duplex caput analogous to the duplex generative system noted postea (p. 285). The abdomen is sessile, i.e., united to the thorax throughout its whole breadth, and composed of twelve segments, of which the five posterior ones form a tail; these latter are segments in the strictest sense, while those of the abdomen proper are, more correctly speaking, articulations covered above and below with transverse horny plates. Articulated to the fifth joint of the tail is a bulb terminating with a sharp curved sting. Poison secreted in the bulb is injected into wounds through two minute perforations near the extremity of the sting. The legs are not very robust, nor long, nor very unequal in length; each consists of seven joints, of which the basal ones (coxae), are fixed to the under side of the cephalo-thorax, and act partly as a sternum; the only portion which can be said to represent a real sternal plate being a very small sub-triangular, or in some genera, quadrangular piece immediately behind the first segment of the abdomen between the extremities of the coxae of the fourth pair of legs (fig. 20, k). These latter are soldered to those of the third pair, the junction being visible as a more or less distinct groove. The coxae of the first and second pairs have angular pieces attached to them, used in manducation, and hence called supernumerary maxillae (fig. 20, o, o, b, b)∙, but while the pieces of the first pair might perhaps be so named, those of the second pair, closing together as they do on their inner margins, rather form a kind of sub-triangular sternal appendage representing the labium, of which there is none properly so-called. Each tarsus ends with two rather long curved superior, and one short straight tooth-like inferior, claws. The first and second segments of the abdomen underneath are almost rudimentary; between them and the anterior edge of the first segment is situated the external aperture to the organs of generation, the horny *plate protecting it being divided longitudinally by a more or less distinct groove. From the second segment, and articulated to it, spring two very conspicuous, curious, comb-like appendages (fig. 20, h, h), composed of a longitudinal shaft of several distinct joints, with a number of slightly curved, bluntish tooth-like processes, fitting closely together, and articulated to their hinder edge, nearly at right angles, like the teeth of a comb. The shafts and teeth of these appendages vary in the details of their form and structure; their use has not yet been certainly ascertained, but their position points to some connection with the process of generation, which is also the opinion of L. Dufour and others; while they have also been thought to be intended to brush away obstructions from the spiracular orifices and other parts; but as in no case are they long enough to reach more than the first pair (out of four) of these orifices, and every consideration of structure is against their being used to clean other parts, this conjectured use is scarcely probable. The spiracular orifices are situated on the under side of the abdomen in four pairs—one pair in a transverse line on each of the third, fourth, fifth, and sixth segmental plates, and are in general easily seen.

The eyes (six, eight, ten, or twelve in number) are placed on the fore part and upper side of the cephalo-thorax,— two, generally large ones, in a transverse line near the middle of the upper part of the caput, the rest (much smaller and varying in size in different genera and species) in two symmetrical groups, one on each side near its fore comers. The falces form, as in other Arachnids, the upper side of the mouth; they are strong, cylindrical, and didactyle, the outer jaw-like terminal claw being articulated in opposition to the inner one; both are toothed, the denticulations varying in number size and form. Below the falces (and forming with the before-mentioned coxrl appendages a complete lower boundary to the mouth) are two strong maxillae, from each of which (as a basal joint) springs a long strong palpus of four joints, the last (digital) joint being more or less bulbiform at its base and didactyle at its extremity. The outer claw is movable, and (like the fixed one) serrate or denticulate on its inner edge. The size and form of this didactyle joint vary in different species and genera; in some it is of enormous size, and its denticulations very strong, while in others it is scarcely larger than the j oint which precedes it. It is the possession, the position, and the office of the exact counterpart of this palpus, which, apart from other considerations, so plainly stamp the affinity of the two sub-orders of the Scorpionidea, in spite of the differences of their respective internal anatomy. Within the mouth parts above noted is a pointed tongue (languette} tipped with hairs.

Internal Structure. —The Muscular System of scorpions is similar to that of other Arachnids. It is well detailed by L. Dufour (Savants étrangers, -χxv. pp. 609- 611), who divides the muscles into thoracic, abdominal, and caudal; those of the abdomen being also subdivided into tegumentary, perforant, and cardiac.

The Organs of Digestion consist of a straight narrow intestine, with little or no dilatation, running from the mouth to the anus, which has its external opening at the lower extremity of the fifth or last segment of the tail. At the junction of the stomachal and intestinal portions the biliary vessels are inserted, and from each side of the former (stomachal part) there issue five narrow casca running into a mass of fatty matter on either side.

The Respiratory Organs, or pulmo-branchiae, have their external orifices or stigmata (as before mentioned) in four pairs on the ventral surface of the abdomen; the pulmo-branchiae, of which one is connected with each stigmatic opening, are hollow sacs, the walls of which are folded into delicate laminae, each being duplex, and all lying one upon another like the leaves of a book; the air is admitted to these through the external openings, which are closed by movable horny lips as in insects. (Jones, Animal Kingdom, 2d ed., 416.) According, however, to L. Dufour (l.c., p. 617), the lips of the stigmata are immovable, and have a varied direction in different species. The air is admitted to the pulmo-branchiae by the action of a linear opening in a supple membrane or diaphragm within the space between the lips and the laminae (L. Dufour, l.c.) Organs of Circulation.— These, according to Newport (Philos. Trans. 1843, pp. 286-298), consist of an elongated, dorsal muscular vessel (or heart) divided into eight chambers, separated from each other by valves, and with auricular openings or valvular orifices, at the division of each chamber, on its dorsal surface. From both sides, and at each end of the dorsal vessel, arteries convey the vital fluid for distribution to different parts of the body.

This dorsal vessel apparently acts in a manner analogous to that of the heart in vertebrate animals. The vital fluid is conveyed back to the “heart” from the pulmo-branchiae, where it has been oxygenated by means of a great number of slender canals, formed by the collection together of vessels that have their origin at the hinder part of the inner side of the pulmo-branchiae. These canals pass round the sides of the body in the hinder part of each segment, and pour their contents into the dorsal vessel through the valvular orifices above mentioned. The conveyance of the fluid from the general circulation to the pulmo-branchiae is effected by means of an intricate system of anastomosing pulmonic and capillary vessels, situated chiefly below the nervous chord on the ventral surface of the body.

From the above L. Dufour (l.c.) dissents. According to his researches, which appear to have been pursued under the great advantage of having fresh as well as living examples to observe and dissect, the heart (or dorsal vessel) is not divided into chambers at all; its chambered appearance, which misled Newport and others, arising from inevitable changes in the form of the organ after death, and long immersion in spirit of wine. Dufour pves very exact figures and descriptions of these changes. According to him the heart is a simple, undivided vessel running throughout the whole body, only narrowing at the fore part of the caput, and in its passages through the tail; and from this tube various lateral veins and arteries issue, those from the hinder or tail portion being profusely branched. He dissents entirely from Newport, Blanchard, and others, with regard to the mode above mentioned in which the vital fluid is conveyed to and from the pulmo-branchiae, but he confesses that he has not been able to find out how it is actually effected, though he believes that the pul mo-branchial laminae are permeated by vascular ramifications spread out over every one of their leaves, and that in these ramifications the fluid receives the benefit of the air admitted to the laminae. Siebold, however, says that no traces of blood-vessels have been found in the pulmonary lamellae of another order, Araneidea; and it is hard to believe but that, if such details as those given by Newport in regard to the scorpion actually existed, Dufour, with the advantage of fresh examples to dissect, should have been unable to discover it. On the whole, it seems too soon, even yet, to dogmatise on the position of the scorpions from their respiratory and circulatory systems. That they have these two systems, the first by means of a dorsal vessel, with lateral branches, the latter by a kind of pouch containing a modification of tracheae, Î3 certain; and that their system is different from that of some other groups is also certain, but in the absence of a more perfect knowledge of the real nature of the difference, its true value cannot well be yet ascertained.

Nervous System.— A longitudinal row of nine—according to Newport, eight—ganglia, connected by a double nervous chord, is situated in the median line of the body, below the intestinal canal. The first ganglion consists of two lobes, the upper one of which, occupying a position somewhat analogous to that of the brain in the Vertebrata, is so called {cerveau) by Dufour. From these lobes the optic and other nerves issue, some of them being connected with the various parts of the mouth and the legs. A nervous collar, according to some authors, surrounds the oesophagus. Dufour, however, disputes the existence of this collar, and explains how the idea of it arose, l.c., pp. 556, 557. Of the remaining ganglia four are, according to Dufour, situated in the abdomen, and from these four there spring on each side and underneath, branching nerves, which run to each of the pulmo-branchiae respectively and their adjacent parts, as well as to the viscera and tissues of the abdomen. The first abdominal ganglion is in close connection with the large thoracic one, and is in some instances so little developed that Newport and others, overlooking it, derived the nerves running to the first pair of pulmo-branchiae from the thoracic ganglion itself, and thence allowed but three to the abdomen.

The caudal ganglia, four in number, do not correspond to the number of segments, which are five, or counting the terminal bulb, six. From each caudal ganglion two lateral nerves only issue, except from the last, whence there issue three pairs; the extra ones, running back, and branching out into the muscles of the poison bulb, doubtless add greatly to its sensibility and irritability.

The Organs of Reproduction occupy, both externally and internally, a similar position in both sexes. The external aperture is duplex, situated between the first and second segments of the abdomen, in front of and, in a manner, between the comb-like appendages, and covered by an operculum. Internally those of the male consist of a duplex set of vessels for the elaboration, collection, and conveyance of the seminal fluid to the external orifices, each orifice having its own set. The vessels, answering to testes, in which the seminal fluid is secreted, consist each of a tube forming three large quadrilateral, flexuose, and free, anastomosing meshes placed longitudinally; those of one set sometimes communicating with the other at the lower mesh by a short, strong connecting tube. According to Treviranus the three meshes on either side anastomose with each other, having, in fact, a common connection throughout, but this L. Dufour considers to be an abnormal case; the vessels for the collection of the seminal fluid, vesiculoe seminales, are three for each set, and all open into the channel of emission; this is produced backwards in the form of a long, fusiform, sheath-like channel, lying along the flanks of the abdominal cavity, and attenuated at both extremities; within this channel is another slender, corneous sheath-like organ, prolonged to the genital aperture, where it is exceedingly fine. This is “le fourreau et l’armure de la verge” (Dufour), and within it is the intromittent organ itself, having a whitish cartilaginous, thread-like appearance. No recorded observations have yet decided the mode in which these parts of generation are used: the Scorpionides being nocturnal in their habits makes such observations very difficult, but all analogy is in favour of copulation by the exsertion and introduction of the thread-like organs above described into the female parts of generation. These consist of two ovaria, each composed of a membranous tube, forming four large quadrilateral meshes in a longitudinal line on each side, anastomosing with each other and with those of the other side; each of these ovaria ends in a simple oviduct (sometimes with, sometimes without ovisacs) leading to the vulva or external orifice. The general similarity of these female organs with those of the male is at once apparent. A curious point noticeable in these parts in the Scorpionides is their duplex character, and hence the question as to their mode of operation becomes of greater interest. It is remarkable that the only other Arachnids in which an intromittent organ is as yet known are among the Phalangides, a group widely separated from the Scorpionides in other characteristic details, though approaching much nearer to the pseudoscorpions. Scorpions are ovo-viviparous, and, according to Dufour (Z.c.), their period of gestation is of great length, extending even to fifteen or sixteen months; but for five of these months, which occur in the winter season, Dufour concludes, from frequent observations, that the whole genital apparatus is, like the animal itself, in a dormant state, and that therefore no progress in the development of the ova takes place during this period. On the very important branch of this subject—the embryology of the scorpion— reference only can be made to the works of Heinrich Rathke, Reisebemerkungen aus Taurien (contained also in Burdach’s Physiology, Bd. ii. p. 242, et seq.) and to that of Dr Elias Metschnikoff, “Embryologie des Scorpions,” Z. Wiss. Zool., Bd. xxi. pp. 204-232, taf. xiv.-xvii.; also separate, Leipzig, 1870.

General Observations. —The sub-order Scorpiones forms a remarkably homogeneous group. It has been divided, however, into several families by Koch {Lie Arachn.); and various genera, based principally on the number and distribution of the eyes, the form of the fore margin of the cephalo-thorax, and the structure of the comb-like appendages attached to the under side of the abdomen, have been characterised. The species are tolerably numerous, but the whole group greatly needs revision, both in respect to its family and generic divisions, as well as in regard to the identification and determination of the species. Those found in Europe are of comparatively small dimensions, and are confined to the southern parts of the Continent; the majority are tropical, attaining their greatest size— nine or ten inches in length—in Central Africa and South America. They are nocturnal in their habits, living by day underneath stones, behind the loose bark of trees, among the ruins and debris of old walls and buildings, and preying upon insects and other Arachnida; they are said to be very partial to the eggs of spiders and insects. It does not appear that they are able to inflict any great injury with the, often formidable looking, crab-like claw with which their palpi terminate, though they can gripe and hold on firmly with them. The wound inflicted by the sting at the end of the tail is certainly more or less venomous; the amount of venom is probably dependent on the age of the scorpion, and the season of the year; and the effect of the sting is no doubt dependent upon the state of health, constitution, or predisposition of the person injured. Experiments, tried by Maupertuis, upon poultry and dogs stung by exasperated scorpions, resulted in their almost entire immunity from bad effects, while in Redi’s experiments, the sting proved fatal in some instances to pigeons. These experiments were tried with European species of scorpion, which would probably be less venomous than those living in tropical countries. For a recent memoir on the poison of the scorpion, and the mode in which it acts, see Dr Jousset, Ann. Ent. Soc. France, 1872, p. 151; also Comptes Rendus, 1870, pp. 407-411. According to Jousset, the venom acts directly upon the red globules of blood, paralysing them, so that becoming agglutinated together, they obstruct the entrance to the capillaries and stop circulation. The peasant inhabitants of Tuscany are said to handle scorpions without fear; but this may be chiefly from a skilful mode of handling them. A scorpion does not appear to be able to move its tail or its sting in a lateral direction, nor does it strike downwards. The present writer has seen natives of Egypt handling large, and it is believed very deadly ones with impunity, but then they always held them tightly by the last joint of the tail. It was a common practice so to catch these creatures, and after breaking off the tip of the sting, to let them loose again; but this infliction generally appeared to produce a kind of paralysis of the whole tail, and probably the poor animal would soon die.

Though the well-known tale of the scorpion, when surrounded by fire, stinging itself to death, has been perpetually repeated, and has even been related to the present writer with some very minute and extraordinary details, it must be held to be merely a “traveller’s story.” Cross-examination, in the special instance noted, very much nettled the narrator at the incredulity which led to it, but it threw more than a doubt over the conclusiveness of the experiment narrated. Probably in some instances the poor scorpion has been burnt to death; and the well-known habit of these creatures, to raise the tail over the back and recurve it so that the extremity touches the fore part of the cephalo-thorax, has led to the idea that it was stinging itself. Perhaps, under the pain of scorching, there may have been convulsive efforts and movements of the highly nervous and sensitive tail in this position, and the point of the sting may even have been inserted between the articulation of the cephalo-thorax and abdomen; and what more would be wanting to make a wonder-loving traveller believe that it had really committed suicide Î The progress of scorpions is neither rapid nor graceful; they are unable to run without elevating the tail to an erect position, which seems to be necessary to enable them to preserve their balance.

Classification of the Scorpiones. —The following is Koch’s systematic division of the scorpions. Order Scorpiones.

Fam. I. With six eyes, Scorpionides.— One genus only, Scorpius (Ehrb.)

Fam. II. Eight eyes, Buthides.— Five genera: Buthus (Leach); Opistophthalmus (Koch); Brotheas (Id.); Telegonus (Id.) ; and Ischnurus (Id.)

Fam. III. Ten eyes, Centrurides.— Two genera: Centrums (Ehrb.); and Vaejovis (Koch).

Fam. IV. Twelve eyes, Androctonides.— Three genera: Andro- ctonus (Ehrb.); Tithyus (Koch); and Lychas (Id.)

One hundred and twenty-two species, distributed variously among the above eleven genera, have been described by Koch (DieArachn.); but many others also have since been added to these, in isolated papers by other authors. For another systematic arrangement, as well as on the group generally, with descriptions of seventy-eight species, see Walckenaer, Ins. Apt., iii. pp. 14-75, where other works are also referred to. Scorpions have been found in a fossil state, as well as in amber, in which substance a species of Tithyus (T. eogenus) has been described by Menge.

Order VI.— Thelyphonidea.

The last group, Scorpiones, seems to be the culminating point of the Arachnids in a certain plane, and it presents the arachnidous type in its highest and most complex state of development. The group now to be considered gradually lowers, so to speak, this type again through its three well-marked families, to the last order Araneidea.

As has been before observed, there is seldom or never in nature exactly the same hiatus between one group and another, as there may be between either of them and others; or, in other words, some groups are far more nearly allied to the one next to it than others are to that next to them, although, perhaps, all of those groups bear the same apparent value in a systematic arrangement. Thus, for instance, the groups A, B, C, D may all be equal in a systematic arrangement, and yet A and B may be far more nearly allied than B and C; or again, C and D may be more closely united than either B and C or A and B. So the two orders of Arachnids—Scorpionidea and Thelyphonidea —are certainly far more nearly allied to each other than, for instance, the Solpugidea and Scorpionidea, or the Thelyphonidea and Araneidea are to each other respectively. So obvious is the affinity of the family Thelyphonidea of the present order to the Scorpiones, that Walckenaer and others have included them in the same order, making a separate order of its other family, Phrynides; but the latter family certainly seems nearer to Thelyphonides than even the Thelyphonides to the Scorpiones; and so, while the Thelyphonides and the Phrynides must go together, these last could scarcely with any propriety be included in the same order as the scorpions. This will, we think, be evident when we consider presently their structural characters. From these and other considerations, it has therefore been thought best to separate the Thelyphonides from the Scorpionides, and include them in another order with Phrynides.

In the order Thelyphonidea, the céphalo-thorax is similar in the general nature and condition of its integument to that of the scorpions, being hard, granulose, and sometimes tubercular, bearing also visible traces of its soldered segments.

The abdomen is segmented, and united to the cephalothorax by a pedicle of greater or less strength, but never, as in the Scorpiones, throughout its entire breadth; it terminates in one family (Thelyphonides) with three postabdominal segments, to which is attached a long multiarticulate setiform tail; in another (Tartarides) with a short tail of different form according to the species; and in the third family (Phrynides) the abdomen terminates with a simple button-Hke segment.

The legs of the first pair are much longer than the rest (in the Phrynides of most inordinate length) and antenniform; the tarsi, and generally the metatarsi, multi-articulate, ending without any terminal claw; the legs of the other three pairs are seven-jointed, with the last, or tarsal joint, subdivided.

The eyes when present (as in two families), are eight in number, placed on the fore part of the cephalo-thorax in three groups, and forming a triangle with the apex (more or less acute) directed forwards; the base of the triangle is formed by two lateral groups, each of three contiguous eyes; the apex by the third group of two eyes near together, but not generally contiguous to each other.

The falces are monodactylous, or terminating with a simple movable fang. The palpi are four-jointed, monodactylous, or rather didactyle in a modified form. The sternum is more developed than in the scorpions, but not so fully as in the next order, Araneidea. The labium is either entirely wanting or very rudimentary in one family, in another fairly developed, and in another altogether absent. In any case, it is probably of small economic importance compared to the labium in the Araneidea.

Such knowledge as is at present attainable in regard to the internal anatomy of this order will be noted in the separate descriptions of each family. These families are three in number,— Thelyphonides, Tartarides, and Phrynides,— and being very distinct, it will be well to give a short diagnosis of each.

Family I.— Thelyphonides. External Structure (figs. 21,22).—The cephalo-thorax is sometimes of a tolerably regular oval form, more or less blunt-pointed before, but often it is of an oblong quadrate shape, also pointed in front, and making not only the hinder part but also the fore part somewhat angular,—the latter having two obtuse lateral angles, and one acute and apical; it is of a flattened form, and destitute of hairs and spines, but is generally granulose, and sometimes covered with more marked, but still minute, tubercles. Marks of segmental soldering are visible, as also a longitudinal groove in the medial line of the caput, similar to, but less marked than, that noted in regard to the scorpions. Beneath the cephalo-thorax are two pieces, which may be regarded as small sternal plates, perhaps the terminal remains representing the complete sternum of the Araneidea. or anticipating its complete form in that order. One of these sternal plates is of a somewhat triangular form, and has its longest or apical angle directed backwards between the basal joints of the first two pairs of legs; the other, more heart-shaped, and with the apical angle reversed, is situated between the basal joints of the legs of the fourth pair. In some species a minute corneous patch may be seen between the coxae, or basal joints, of the third pair of legs, affording still further evidence of the remains of a sternal plate. At the centre of the fore margin of the foremost of these sternal plates is a small point which seems to represent the labium. Beneath the fore part of the cephalo-thorax are two not very powerful falces, terminating with a long, powerful, movable, curved fang, somewhat resembling what we find in the Araneidea, and hinting at a transition to that order from the didactyle falces of the Scorpiones. Beneath, and opposed to, this fang is a fixed tooth-like claw; these parts of the mouth are thickly clothed and fringed with hairs. Immediately in front of the fore sternal plate, beneath the anterior part of the cephalo-thorax, are articulated two enormous maxillae of a subtriangular form, the apex being at the articulated part, and the inner basal angle prolonged into a larger or smaller tapering, pointed apophysis, which is now and then denticulate. From the extremity of each of the maxillae springs a proportionately strong and massive four-jointed palpus, powerfully armed with spines, denticulations, and claw-like projections; the inner extremity of the last, or digital, joint terminates like the radial (or the joint next before it), with astrong, claw-like, sharp-pointed projection, in imperfect opposition to which there is a stronger movable claw, of the same nature, articulated to the outer extremity; the fixed claw of the digital joint, with the joint itself, appears capable of being opposed at will to the fixed claw of the radial joint, thus giving the palpi a duplex kind of didactyle claw,—didactyle, that is, in a modified sense, differing as it does considerably from the terminal claw of the scorpion’s palpus, which is more properly spoken of as didactyle. The movable finger of this claw would, perhaps, be more correctly reckoned as a substantive joint, terminating with a more or less sharp corneous nail; and this joint, opposed to a pointed apophysis of the one to which it is articulated, forms the so-called didactyle claw; in fact, the terminal palpal claw of the Scorpiones (including the Pseudo-Scorpiones) as well as that of the Phalangidea, appears to be similarly constructed. In the present family, however, the basal portion of the joint, bearing the fixed claw, being far less developed (seldom stronger or more bulbous than the other joints), and the two fingers being always of unequal length, the didactyle nature of the whole is less real, and less apparent; while in the scorpions its bulbous form is generally apparent, and often inordinate, the equal length of the two fingers and their evidently purposed opposition to each other making the claw, in the fullest sense, didactyle.

If this view (that the movable finger of this claw is a substantive joint) be correct, the palpi in the present order, as well as in the orders Phalangidea and Scorpionidea, must be considered to have five instead of four joints, thus bringing them to an equality in this respect with the Araneidea. The palpi in the third family of this order— Phrynides—bear out this idea strongly.

The legs are long, slender, and seven-jointed, except those of the first pair, which have but six, the genual, or fourth, joint being absent. The tarsi of the first pair are divided into eight short articulations, while those of the rest have but three. There is probably some variation in the number of these articulations in different species, since Walckenaer describes the tarsi of the three hinder pairs as 7⅛ojointed; the first pair are far more slender than the rest, palpiform, and without any terminal claw; they appear, as it were, to be thrust out of their position by the great size of the maxillae, and their basal joints seem to be jammed in over those of the second pair. The tarsi of the three hinder pairs terminate with three claws, of which those of the superior pair are the strongest and curved.

The abdomen is of a long-oval form, composed of nine quasi segments, formed by a covering, both above and below, of so many transverse articulated corneous plates; while the cartilaginous membrane on each side, between the lateral margins of the upper and lower plates, is continuous, not folded or articulate as in the Scorpionidea. This is a point to be noted, as it marks a transition to the abdominal type of the Araneidea. The first plate on the upper side forms a protective covering to the pedicle by which the abdomen is united to the cephalo-thorax, and makes the pedicle look broader than it really is. There is a double longitudinal row of impressed circular spots on the upper side, two (in a transverse line) on each corneous plate, except the first and last; these impressed spots are perhaps points of attachment for muscular fibres.

Beneath the abdomen, on the fourth and three following segmental plates, are eight stigmata in as many largish, shallow, circular impressions; they are, however, imperforate, and are probably, like those mentioned above, points for the attachment of muscles. The spiracular stigmata are four in number, two being placed beneath the hinder margin of each of the first and second sub-abdominal plates, one on each side of the median line; the genital aperture is under the hinder margin of the first plate, between the first two spiracular openings. Joined to the posterior extremity of the abdomen are three small cylindrical, postabdominal segments, to which is attached a long setiform tail, variable in length, composed of a number of small articulations, and, like the legs and palpi, sparingly furnished with hairs; at the extremity of the third post-abdominal segment, beneath the tail, is the anal opening.

The eyes are eight in number: two placed transversely, near to each other, on the fore margin of the caput in the medial line, and three others in a triangular group on each side at its lateral angles, just above the insertion of the legs of the first pair.

With regard to the Internal Structure of the Thely-phonids but little appears to have been ascertained. The respiration is pulmo-branchial; the spiracular apertures being, as above stated, four in number, and situated in the position already mentioned. Their mode of reproduction is probably like that of the scorpions, ovo-viviparous, but this is conjecture only.

General Observations. —The family Thelyphonides is exceedingly homogeneous, and comprises but a single genus, Thelyphonus (Latr.), of which twenty-nine species only have been recorded and described,—twenty-six in one of the latest works upon them, by A. G. Butler, Ann. and Mag. N. II. 1872, vol. x. pp. 200-206, and Cistula Ento-mologica, 1873, part vi. pp. 129-132; and three others in a still more ιeceut paper by the late Dr Stoliczka, Journ. As. Soc. Beng., part ii. No. 2, pl. xii.

All the species of this small but remarkable group are confined to the tropical regions of Asia, America, and Australasia, no species having yet been recorded from Africa. In size they vary from rather more than half an inch to 2 or 3 inches in length. Among other characters useful in the identification of the species, are the number and differential development of the various processes and denticu-lations of the palpal joints. Of their habits little io known, and much of that little is of a very recent date. Dr Stoliczka (l.c.') gives a short account of them, from which it appears that they are nocturnal or crepuscular, living by day in damp places under the bark of old trees; when disturbed they hold up the palpi, as if for defence, and beat a rapid retreat, with the tail in an erect position. In this position of the tail we see a curious relationship to the scorpions, but apparently without the same necessity, in the present instance, for such a position. They lie still when uncovered, evidently simulating (though of course unconsciously) a fragment of old bark or fungus. The first pair of legs act more as feelers than as organs of locomotion. In the presence of a sternal plate, the mode in which the abdomen is united to the cephalo-thorax, and the structure of the falces, Thelyphonids approach nearer than the scorpions to the structure of the true spiders, and, as we shall see, the family Phrynides is a transitional group bridging over some part of the gap between the two, while in the massive palpi (though imperfectly didactyle), and in some other respects, they show an unmistakable alliance to the scorpions.

Family II.— Tartarides.

This family is nearly allied to the former—Thelyphonides—but has a more elongated form. The cephalothorax is beak-like in front, and is also divided into two parts or segments; the first comprises the caput, and ths coalesced thoracic segments belonging to the first two pairs of legs; the hinder part is the smallest, and comprises the second thoracic segments belonging to the third and fourth pairs, but no grooves or indentations mark the union of the segments, its surface being smooth and glossy. The abdomen is united to the cephalo-thorax by a stout pedicle, and is covered above and below, as in Thelyphonides, with eight or nine transverse, corneous, articulated plates, the upper series separated from the lower by a narrow divisional space, covered with a continuous cartilaginous integument. Beneath the fore part, at the hinder margin of the first sub-abdominal segment, a line-like fissure in the median line probably represents the opening to the reproductive organs; near the fore margin of each of the fourth, fifth, and sixth plates, in a transverse line, are two small elongated stigmata, thought at first to belong to the respiratory apparatus, but further examination seems to prove them to be, like the eight analogous stigmata in Thelyphonides, imperforate, and probably due to the same cause conjectured in regard to them. Two (or four) narrow slits, placed two and two symmetrically on each side of the genital aperture at the fore margin of the first and second segments, but very difficult to be correctly ascertained, are probably the external openings to the respiratory organs; these points, however, can hardly yet be said to be satisfactorily determined. Two or three very narrow corneous rings, or post-abdominal articulations, support a caudal appendage, either slender, cylindrical, and bi-arti-culate, or of a largish, peculiar, sub-triangular form, articulated to a small foot-stalk. Eyes none, no traces even of eyes being visible. The falces are strong, of a flattened cylindrical form, deeper than broad, projecting in the plane of the cephalo-thorax, and terminating with a sharp, curved, movable fang at their upper extremity, the lower extremity being rather pointedly prominent.

The palpi are very strong, five-jointed, and each issues from a long, strong, nearly cylindrical basal joint or maxilla, the inner fore corner of which is prolonged into a sharp, strong point; the other joints are armed variously with teeth, and the final, or digital, joint in one species has a longish, but not very strong, spine beneath it, terminating with a small, apparently movable, curved claw. In these palpi we see a marked transition from the more apparent didactyle nature of those of Thelyphonides to those of the Phrynides, removing them further than the former, in this respect, from the Scorpiones.

The legs appear very similar to those of Thelyphonus; they are seven-jointed; those of the first pair are slender and evidently palpiform; their tarsi are composed each of several (apparently ten) minute articulations, and devoid of terminal claws. Those of the other three pairs are apparently inarticulate, and each ends with three simple curved claws, of which the inferior one is the smallest and most sharply bent; the femora of these three pairs are all strong, those of the fourth pair inordinately so. The sternal plates are very similar to those of Thelyphonus, but the hinder one is not so much developed, and the central corneous spot is not visible.

This family, of small but exceedingly interesting blind Arachnids, contains but one at present known genus— Nyctalops (Cambridge), and two species— N. crassicaudata (Id.) and N. tenuicaudata (Id.); both are of a uniform pale yellow-brown colour, differing from each other, among other characters, in the markedly different form of the tail; the length of the largest (probably, but not certainly ascertained to be, in the adult state) is but 2 J lines. They are found under decayed leaves in Ceylon; but nothing is yet known of their habits, nor of their internal structure and anatomy; analogy, however, points to a similarity in this latter respect to Thelyphonus.

Family III.— Phrynides.

This is also a remarkably homogeneous family, and although, undoubtedly, a near ally of the Thelyphonides, yet in its form it presents many typical characters of the Araneidea (figs. 23, 24, 25).

With respect to External Structure, the body is short and broad instead of elongated, as in Thelyphonus and Nyctalops. The céphalo-thorax is flattened, of a round oval form, hollowed on the hinder margin, and often of a short heart or kidney shape; its integument is hard, horny, granulose, and often tuberculose; near the centre is a deep fovea, or pitlike indentation, from which other grooves and indentations radiate, showing the, now soldered up, junctional lines of the caput and thorax, and thoracic segments. In these characters of the cephalo-thorax the affinity of Phrynides to the Araneidea is very plainly indicated, as it is also in the sternal plate, around which the legs are articulated.

The falces are strong and somewhat cylindrical in form. They project in a line parallel to that of the cephalo-thorax, and each terminates with a strong curved denticulated fang, which is articulated to its upper extremity. The falces are toothed also on their under sides; the denticulations of the falces and their fangs differ a good deal in different species, and form one of the best and most tangible characters for the determination of the species (see a paper on “Phrynus,” by A. G. Butler, in Ann. and A fag. N. H., Aug. 1873, pp. 117-125, pls. 6, 7). In the usual position are two strong divergent maxillae, each with a broad obtusely rounded apophysis at the fore extremity on the inner side; from the extremity of each maxilla springs a long, strong palpus, in some species of great length, consisting of four or (reckoning the large terminal movable claw as a substantive joint) five joints. This palpus is armed variously with tubercles, spines, and denticulations, especially on the cubital and radial joints, where several long, strong spines, opposed by the terminal claw (or digital joint), form a powerful grasping or raptorial organ, but one considerably further removed than the analogous portion of structure in

Thelyphonus from the didactyle claw of the Scorpionidea. Between the maxillae, and issuing from the fore margin of the sternum, is a narrow, elongated tapering labium, id some species bifid at its extremity; the presence of a distinct sternal lip, or labium, is another mark of affinity to the Araneidea.

The legs (seven-jointed) are long and generally slender, though the coxal joints of the three hinder pairs are long and strong, and articulated laterally to the sternum. The legs of the first pair are palpiform, and of great length and tenuity, the three terminal joints forming one long slender tapering portion, which is however subdivided into a great number of minute homogeneous articulations without any terminal claw; each tarsus of the remaining three pairs is divided into three articulations, ending with two curved claws; and in some species the tibial joint of the fourth pair is also tri-articulate. Probably the subdivision of the fourth pair of legs varies in other species also. The coxal joints of the first pair are, as it were, crushed in behind the maxillae and above the coxae of the second pair, as in Thelyphonus. The extreme articulation of each tarsus has a peculiarity never (it is believed) noticed before; its upper side being covered, throughout its length, with a separate integumental plate, prolonged at its fore extremity into a corneous, slightly bent, claw-like apophysis, forming a kind of third claw above and between the two ordinary ones. These latter spring from a supernumerary or heel joint, which has a short, conical, tooth-like spur beneath it, representing the usual third claw in other groups.

The eyes, eight in number, are placed in three groups, forming a very obtuse angled triangle on the fore margin of the caput. Two eyes, seated transversely, and near together in the medial line, constitute the apex of the triangle, which is directed forwards; the other two groups are of three eyes each, closely grouped in a triangular form, one on each side, about parallel with the second pair of legs.

The abdomen, is oval, of a somewhat flattened form, and joined to the cephalo-thorax by a narrow pedicle, showing, in this also, a near approach to the Araneidea; it consists of ten quasi-segments, or articulations, formed, as in the other families of the order, by a series of upper and lower transverse corneous plates, having an, apparently continuous, cartilaginous integument between the two series of plates, and terminating with a button-like joint, or process, at its extremity. On the under side are two parallel rows of impressed spots, two, in a transverse line, in each of the fourth and three following sub-abdominal plates; but, apparently, like the corresponding marks in Thelyphonus, imperforate. The organs of generation have their external orifice beneath the posterior margin of the first subabdominal plate; and the external openings to the respiratory organs, four in number, are situated, two beneath the posterior margin of the first, and two others beneath that of the second of these plates. The sternum, is oval, and often superficially divided into several portions by various ridges and indentations.

With regard to the Internal Structure of the Phry-nides, the respiratory system is pulmo-branchial, the orifices to these organs being four in number, and placed as above mentioned.

The nervous system, according to Van der Hoeven, appears to be very simple, consisting of a large thoracic bi-lobed ganglion, from which four pairs of lateral nerves issue, while a double nervous chord runs back through the connecting pedicle into the abdomen, where it divides into two divergent branches, from which the various nerves are distributed to the different parts of the abdomen.

General Remarks. —The family Phrynides comprises but one genus, Phrynus (Olivier), which, according to the most recent publication upon it (A. G. Butler, l.c. supra), includes twenty species only, all confined to the tropical regions of the world. The individuals of most of these species appear to be of rare occurrence, or; at least, but rarely observed, and the family has, comparatively speaking, received but little attention. It is, however, one of great interest and importance, and deserves more elaborate and careful treatment, especially in regard to its habits and internal anatomy, for it undoubtedly forms a plain passage from the Scorpionidea (through Thelyphonus and Nyctalops) to the true spiders (Araneidea). The main external marks of affinity with this order have been noticed in speaking of the different portions of external structure of the Phrynides.

Order VII.— Araneidea.

We have come now, by an easy transition from the Phrynides, to the last order of Arachnids— Araneidea or True Spiders (figs, 26, 27, 28). And first, with regard to their External Structure, they consist, like others of the sub-class Arachnida, of a body divided into two parts —cephalo-thorax and abdomen; but these are united only by a slender pedicle, and neither is segmented, ringed, or articulated, nor (in respect to the abdomen) covered with horny plates, except in two instances— Liphistius desultor (Schiödte) and (but partially only) Tetrablemma mediocula-tum (Cambridge), both exceedingly rare and remarkable species. The céphalo-thorax, though undivided, yet shows by its various, and more or less strongly marked, converging grooves and indentations, that it is composed of the ordinary cephalic and thoracic segments soldered together; and although these segments form but one undivided portion of structure, it is necessary to speak of it frequently by the names of its two portions—caput and thorax. The caput is almost always easily traced, forming a kind of wedge-shaped portion, jammed (as it were) into the first of the thoracic segments, and giving one the idea, in most cases, of its fore part having been to a greater or less extent truncated or lopped off (fig. 28, δ). Similarly the last of the four thoracic segments has the appearance of having been driven in to meet the caput, all the segments thus converging, on the upper side, towards a common fovea, or more or less deep central indentation (fig. 28, e), and on the under side forming a sternum (or sternal plate), in which, however, no appearance of segmentation is generally visible beyond small eminences opposite to the articulation of the legs, with which the number of the thoracic segments, as seen above, agrees. The integument of the cephalo-thorax is either hard, horny, or coriaceous, generally more or less clothed with hairs and bristles, and sometimes, though more rarely, with tubercles and spines; occasionally it is perfectly smooth and glabrous. The eyes, when present, are two, four, six, or eight, and are very variously, but always symmetrically, disposed on the fore part of the caput (figs. 28, 29, 30). The number and general position of the eyes form valuable characters for the formation of genera; while their relative size is strongly characteristic of species. The eyes of spiders, like those of other Arachnids, are always simple.

The leys, eight in number, are articulated to the sternal plate (mentioned above) which forms the under side of the cephalo-thorax; in one genus, however (Miagrammopes, Cambr.), found in Ceylon and Australia, no sternum properly so called exists, the legs being articulated to the continuous under side of the cephalothorax. Except in one or two species the legs are seven-j ointed, and variously furnished with hairs, bristles, and spines. Many spiders have a kind of pad of closely set papillae-form hairs beneath the extremity of the tarsi of some or all the legs, and often extending along the whole of the under side of the joint. This pad enables the spider to run over smooth vertical surfaces, acting as a kind of sucker, partly by atmospheric pressure, and partly (Mr Blackwall thinks wholly) by means of a viscid secretion from the papillae-form hairs. Each tarsus ends with either two or three more or less curved or bent claws, commonly (but not always) pectinate or finely denticulated; these (with other opposed serrated claws, in some groups) are used in traversing their webs, and as hooks to give a tension to the line of their snares by alternately pressing and straining upon them; the spines and bristles are used also in many cases in the actual construction of the silken snares in which spiders entrap their prey. The spines on the legs of some spiders which excavate cylindrical holes in the earth (lined with silk and closed with a hinged lid) are very strong, and well suited for digging out the soil. The males of some species, again, have a curious row of short, closely set, curved, spiny bristles along a portion of the upper side of the metatarsi of the fourth pair of legs; the use of this row of bristles (called the calamistrum) is alluded to further on. The length of the legs in spiders (both actual and relative) is very various; and the differences between them, as well as their armature and terminal claws, furnish valuable characters, often generic, and always important in the determination of species.

The falces, two in number, are articulated immediately below the fore margin of the caput; their direction is various, ranging from a line parallel to the plane of the cephalo-thorax to one perpendicular to it; they are in general opposed to each other, and in most cases are armed with teeth on their inner surface, especially towards the extremities; each also terminates with a movable curved fang, which, when not in use, is (according to its mode of articulation) folded down either across the inner side of the extremity of the falx, or (as in one extensive family, Theraphosides) backwards along its length; by means of these fangs, which are internally channelled and perforated at their extremities, a poison secreted within the caput is instilled into the wound made by them, proving, no doubt, fatal to the spider’s prey, and often nearly so to human beings. Not to dwell upon the, probably exaggerated, accounts of the Tarantula, there are well-authenticated instances of recent date in regard to the very deadly nature of the poison of quite a small spider, Lathrodectus Katipo (LL Powell), found in New Zealand (Trans. 2V r . Z. Instit. iii. p. 56; also Id. ii. p. 81, and iii. p. 29). A larger European species of the same genus, L. oculatus (Walck.), also bears the reputation of being venomous.

The maxillae are a conspicuous, as well as an important, portion of structure in the Araneidea; they are two strong pieces situated immediately behind the falces, exceedingly varied in form and strength, and articulated to the fore side of the sternum between the basal joints of the first pair of legs. Their real direction is always divergent, t.e., outwards from each other, but as in most cases the inner extremity is produced into an apophysis of greater or less size (sometimes following the direction of the maxilla, sometimes curved so that its extremity almost touches that of the opposite maxilla), the maxilla itself often seems lost in the part which projects from it. Owing to this, the palpus which springs from each maxilla, although really always springing from its extremity, appears more frequently to issue from its outer side; and, in fact, it can hardly in those cases be described (without leading to some confusion) as issuing in any other way. The form of the maxillae, together with the apparent point of palpal issue, constitutes one of the most valuable characters for the establishment of genera.

The palpi, issuing from the maxillae as just described, are two (in both sexes of many, and in the female sex of most species, leg-like) limbs, of five or (counting the basal joint—maxilla—to which each is articulated) six joints; in the female spider the palpi generally end with a single, and sometimes denticulate, curved claw; in some instances, however, there is no terminal palpal claw; but in the male, the third (cubital) and fourth (radial) joints of the palpi are (the former often, the latter always) characterised by prominences, spiny apophyses, or protuberances, which furnish some of the strongest, as well as most tangible, specific characters of that sex; the last (or digital) joint of each palpus (in the male spider) is generally more or less concave, and always includes, either within its concavity or articulated to its under side, a (frequently complex) congeries of corneous lobes, spines, and spiny processes, in some instances articulated to each other so as to be capable of being opened out as by hinges. These are not developed until the spider arrives at maturity. Up to that period the digital joint has a tumid and somewhat semi-diaphanous appearance, and, although commonly smaller, bears the same general form that it has after maturity. These processes, or, as they are called, palpal organs, are connected with the process of reproduction—the fecundation of the female. This subject, however, we shall have occasion to refer to again. The palpi are generally furnished more or less with hairs, bristles, and spines, like the legs; and like them, also, are reproduced after accidental loss.

The labium is also another important portion of structure; it is situated at the fore extremity of the sternum, between and in front of (or rather beneath) the maxillae; it is of varied form and size, and stopping the gap between the maxillae, it completes with them the inferior and lateral boundaries of the mouth, the falces forming its upper limits. The labium is always present, except in a new and very remarkable Brazilian spider, Aphantochilus Rogers™ (Cambr.), in which the labium is wanting, and yet not wanted, because the maxillae, in this instance, close up to each other, leaving no gap between them.

Between the labium and falces is another portion of structure, the tongue; it is, no doubt, by the aid. of this that the act of swallowing the juices of insects, when expressed by the falces and maxillae, is effected; that, in fact, the spider eats without being choked. No use hitherto has been made of the tongue in spiders for purposes of classification, but the form of the labium, is very useful for the characterisation of genera. These parts —falces, maxillae, labium, and tongue—thus complete the mouth-parts of a spider.

The sternum, has already been mentioned; its form varies from oval to heart-shaped, and sometimes somewhat pentagonal; its convexity also varies considerably; its use in classification is rather limited, but with its clothing of hairs, bristles, or pubescence, or its sometimes glabrous nature, it generally has some specific importance. In one known genus only, as mentioned above, is the sternum wanting.

The abdomen is exceedingly varied in form in different families; it is united to the cephalo-thorax by a short narrow pedicle, and generally terminates writh organs for spinning; in one species, Liphistius desultor (?) (Schiödte), the spinners are placed near the anterior part of the under side of the abdomen; and in another, Mutusca mammosa (Cambr.), one pair only are so placed, the rest occupying the ordinary position. The number of spinners varies— two, four, six, or eight; they are placed in pairs, and when a fourth pair is present it is, usually as a single one, united throughout its length (but with often a line of division visible), and occupying a transverse position in front of the rest. It is but very lately that spiders have been observed with two spinners only; see “Spiders of Palestine and Syria,” O. P. Cambridge, Proc. Zool. Soc. 1872, p. 260; Ann. and. Mag. N. H. 1870, pp., 414-417, Ibid.

The spinners consist of from one to three joints, and vary greatly in size and structure, as well as in number, but their use in classification has not hitherto been as great as might have been expected; generally they are separate, but in Tetrablemma (Cambr.) they are enclosed in a kind of corneous sheath. Those of the fourth pair when present (which they are in both sexes) are correlated, but in general only in the female sex, with the calamistrum, or double series of curved bristles before mentioned, on the metatarsi of the fourth pair of legs. The function of the calamistrum has been proved by Mr Black wall to be the carding, or teasing and curling, of a peculiar kind of silk, secreted and emitted from the fourth pair of spinners; when thus prepared this silk becomes adhesive, from its minutely divided and elastic fibres; and, disposed about the lines of the spiders’ snares, it renders more easy the entanglement and capture of their prey. Immediately above the spinners is a small nipple-like prominence which indicates the anal orifice.

The abdomen is covered with a continuous integument neither annulate nor segmentate; in one species, however (before mentioned), Liphistius desultor (Schiödte), the upper side has a longitudinal series of transverse corneous plates, like those of the Phrynides; and something of a similar kind, but less marked, is observable in Tetrablemma medioculatum (Cambr.), a very rare and remarkable little spider found in Ceylon. The epidermis of the abdomen is of various kinds and consistency in different groups, sometimes excessively thin and tender, at other times tough and coriaceous, and sometimes hard and horny, with a varied armature and clothing of hairs, bristles, pubescence, tubercles, and spines, sometimes being, however, perfectly bare and glabrous; its colours, also, and the patterns produced by their distribution, vary exceedingly. Underneath the fore extremity of the abdomen are placed tho external openings to the respiratory organs; these apertures consist of a narrow slit or orifice under the fore edge of round or oval scale-like plates, placed on each side of thα median line; such plates are in some spiders four in number, but for the most part only two. Other spiracular openings also exist in many spiders, both at the anterior part of the under side (fig. 28, t, t) and near the spinners (Siebold), but these are usually far less perceptible than the others before mentioned, and often discoverable with great difficulty. The ordinary pair of spiracular plates are in general very conspicuous, commonly differing in colour from the surrounding surface, and sometimes slightly pubescent. They occupy each side of the median line at the extreme fore part of the under side of the abdomen; and between them is, in the male spider, a very minute orifice which leads to the seminal organs; while in the same situation in the female is an aperture usually rather conspicuous, always of characteristic form, and often furnished with a corneous process of greater or less development. This aperture is the vulva, and the process (when present) probably has the function of an ovipositor. The form and structure of this aperture is of great use in the determination of species, but until the female spider attains maturity no aperture at all is visible. The orifices to the breathing organs are fringed with hairs or lashes, and open and close by an internal muscular arrangement. The other pair of spiracular plates, when present, are in some cases close behind those just above mentioned, but more commonly at some distance further towards the hinder extremity of the abdomen.

On the upper side of the abdomen may be seen in many spiders several impressed spots or dots, differing in number and position in different genera and species, but always placed symmetrically. These, considered by Treviranus as stigmatic openings, are probably indicated points of fixture for muscles beneath the integument, being apparently imperforate. Smaller puncture-like marks are also often visible on the under side, and are perhaps similarly caused. The hairy clothing of the abdomen (as well as of the cephalothorax and other parts), variously tinted and coloured, gives the specific pattern to the spider from its diversified distribution; and when such clothing is absent, the pattern is often equally distinct and varied, arising in such cases from a pigment in the coats of the integument itself.

Internal Organisation. —The Muscular System of spiders is very similar to that of the rest of the Articulata. The muscles are formed of numerous parallel fibres traversed by very marked striae; these muscles are attached to the different portions of the tegumentary system, and move the various parts of the body by the contraction of their fibres. Those which set in motion the falces, the maxillae, and the coxae of the legs, are attached to the thorax, and radiate to all these parts from a centre, marked externally by what has been before spoken of as the thoracic indentation, or fovea. The other joints of the legs move, one after the other, by means of small and exceedingly fine muscles, of the two kinds ordinarily known as extensors, to raise the joint, and flexors, to lower it. All these muscles act with great rapidity, and enable the legs to move in every direction according to the mode in which the various joints are articulated. The differences in the relative strength and volume of the muscles are very great; those, for instance, by which the fangs of the falces are moved are exceedingly powerful; the abdomen being generally soft, its integument does not furnish such firm points of attachment as that of the thoracic region, and yet the spider can move its abdomen with the greatest ease in every direction. Beneath the integument, at the fore part of the under side, two ligaments are attached to a membranous plate, situated under the branchial operculum, and at the hinder part, round the ring which encircles the spinneΛ and the anus. The fore half of these ligaments is cartilaginous, while the hinder half is composed of contractile muscular fibres, and by means of those muscles the spider moves its abdomen. Two other pairs of muscles may also be particularly mentioned,—one pair inserted under the membrane in the junctional pedicle, the other leading round the respiratory organs: the office of these is to open or close the branchial opercula, and to draw the sexual organs backwards or forwards. The spinners are moved by special muscles similar to those of the legs. (Simon, Hist. d. Araignf

The Organs of Digestion consist of a large sac, or stomach placed in the cavity of the cephalo-thorax, and fastened to its arch by a strong muscle; this muscle passes round and through the stomachal sac; into the stomach a tube (oesophagus) leads from the mouth, and from it ten lateral branches or caeca (five on either side) issue, passing down the sides to the origin of the legs, and, curving round, end in a reservoir placed below the stomach. This reservoir is connected with the stomach by the muscle mentioned above, and divided from it by a solid plate into which this muscle is inserted; it, in fact, forms a kind of second or lower stomach into which the juices forming the spider’s food are forced from the upper one by muscular action.

Out of the stomach the alimentary juices go into a tube or intestine, which is much contracted in size in passing through the junctional pedicle into the abdomen, but enlarges a little within the latter; this tube curves over for some distance in a line parallel with the dorsal integument; it then drops down suddenly, forming a large loop, and so passes into a large rounded pouch (rectum), in which the undigested portions of food collect, and thence pass out through the anus, situated, as before observed, at the extremity of the abdomen just above the spinners. The abdominal intestine is imbedded in a mass of fatty globules, from which bile is secreted; the bile passing by means of biliary ducts (into which urinary organs also pour their contents) into the rectum. Digestion is effected by means of a gastric juice secreted by appropriate glands between the lateral caeca, and thence poured into the stomach (Simon, l.c., after Dugès).

Walckenaer, Ins. Apt., following Treviranus, gives a slightly different account of the digestive apparatus of Tegenaria domestica ( ∖Valck. ) Probably a certain amount of variation would be found in the details of form and structure of the stomach and intestinal canal, and other organs of digestion, in different species; but the general plan of the digestive arrangement is the same. It is an undecided question whether the oesophagus of spiders can pass any substance except the juices of their prey. See O. P. Cambridge in Entomologist, May, 1870, pp. 65-67; and√4nn. and Mag. N. H., Dec. 1872; and F. Pollock, Id., Oct. 1872.

Organs of Circulation.— As in some other groups of Arachnids a strong muscular tube or vessel (divided into four chambers) runs along beneath the dorsal integument of the abdomen, following the integumenta! curve; this dorsal vessel (or heart) varies in form in different species, and is enveloped in a fine fibrous tissue, which forms a jrøricardittwi. The several chambers of the heart communicate with the pericardium by means of small elongated orifices (auriculo-ventricles) placed at the constrictions where the chambers are separated from each other; through these orifices the vital fluid passes into, but cannot pass out of, the heart. This latter operation is effected by the contraction of the heart, which forces the fluid forwards into a tube or artery issuing from the first chamber; this tube—aorta—passes through the junctional pedicle, and entering the thorax, divides into three paire of arteries. The upper pair follow the dorsal line and give off blood-vessels to the eyes, the falces, and other parts of the mouth; the second pair, intended to give nourishment to those parts, pass over the stomach; and the third are imbedded beneath that organ, and emit arteries to the legs, extending to the very extremity of each. These three pairs of arteries reunite forwards and form a collar round the cerebral ganglion; and from thence a tube —abdominal or posterior aorta—passes backwards under the ganglia through to the abdomen, continuing quite to the spinners; this tube furnishes numerous branches to the organs which it passes in its course. From the general circulation the vital fluid is brought into two large longitudinal reservoirs within the lower face of the abdomen, by means of sinuses or canals formed by the interstices of the muscles; these anastomose and pour their contents into the reservoirs just above mentioned; from them the fluid penetrates the branchial organs, and being there reoxygenated, is carried back to the pericardium by four brancho-cardiac vessels; from thence it passes into the dorsal vessel or heart through the auriculo-ventricles above named. Muscular contractions and dilatations appear to be the means by which the fluid is propelled through the sinuses that bring it to the branchial organs for oxygenation (Simon, l.c., after Emile Blanchard, and Dugès).

As has been already observed in several notes, there is some difference between the above account of the circulatory system and that given by Claparède; probably the organs of circulation vary somewhat in different species. One point of difference, however, between the above and Claparède’s description is of importance, that is, the difference which is mentioned in note (4) below. The idea that the blood “penetrates” the branchial organs may have been led up to by the apparently unfounded, but confidently pronounced opinion that these organs were true analogues of the lungs of the Vertebrata; whereas, if the blood does not penetrate them, but is merely oxygenated in its general passage by and round them, their real tracheary nature (as seems to be the better opinion now) is strongly confirmed; and hence the hitherto widely-received division of Arachnids into pulmonary and tracheary, based upon the idea of the distinct nature of the pulmo-branchiae from the tracheae, falls to the ground; the more especially since, whatever the difference may be between the ordinary tracheae and the pulmo-branchiae, both are found in the same individual, in the order we are now considering —Araneidea.

Organs of Respiration.— From what has just been said, it seems hardly proper to base any definition of the respiratory organs of spiders on the supposed essential distinction between the pulmo-branchiae and tracheae. Such difference as there is, and it is indeed an important one, seems to be this, that whereas the tracheae are lengthened tubes, which convey the air in very small volumes to different parts of the body, and so oxygenate the vital fluid in its passage, the pulmo-branchiae are modified tracheae, localising, so to speak, within a peculiarly furnished sac, a considerable volume of air in the immediate course of the large sinuses, in which the used-up vital fluid is re-collected previous to its return to the dorsal vessel. This arrangement, no doubt, marks a higher state of organisation than is possessed by those Articulata furnished with merely simple tracheae; it is a progress from a diffused to a localised system, but still it seems essentially distinct from the lungs of vertebrates, in which the blood is carried to the air and permeates every portion of the air-vessels, and not the air to the blood, as is really the case in regard to both the pulmo-branchiae and tracheae of spiders. It is not a matter, perhaps, of prime importance, but if the above views be correct, it would seem better to relinquish the name of pulmo-branchiae, since there is not only no real analogy to the lungs of a mammal, but just as little to the gills of a fish. We would propose, therefore, to distinguish these modified and localised tracheal sacs by the name of sac-tracheae, the ordinary ones being designated tube-tracheae.

In some spiders, Theraphosides (including the giant spiders of the family better known as Mygalides), the respiratory organs are solely sac-tracheae; these are in this case four in number, and placed in two pairs on the lower side of the abdomen. Their external orifices are protected by spiracular plates (as before noticed); in other spiders there is, close in front of each of the fore-pair of sac-tracheae, an orifice leading to tube-tracheae. In some few spiders a kind of supernumerary spiracular slit or opening is visible near to the ordinary one, but not always similarly placed. A pair of others are also visible close behind the sexual aperture in Cambridgea fasdata (L. Koch) (fig. 27, t, t). These openings probably lead to other tube tracheae. We have also noticed slit-like openings similar to those above mentioned in some undescribed species of Drassides, and some also exist in the well-known European spider, Argyroneda aquatica. Tracheal openings also exist, according to Siebold, near the spinners. The sac-tracheae of spiders are of the same construction as the organs described as pulmo-branchiae in the family Scorpionides. The following short description is abstracted from E. Simon, l.c. l following Emile Blanchard:—“The respiratory apparatus is contained in sacs beneath the stigmata; these sacs are globular and flattened, formed by a silvery white membrane. Each of them contains a body not fastened to the walls of the sac, but lodged as in a chamber; this body is composed of sixty or seventy plates (lamellae) lying one upon another like the leaves of a book. Each one of these apparent plates is in fact itself a flattened sac, with an opening on its lower side communicating with the outer air admitted through the spiracular orifices. The walls of these numerous sacciform lamellae consist of two membranes of different composition, the inner one hard, the other soft, and between them is a very fine strong network analogous to the spiral thread of the tracheae of insects.”

The inspiration and expiration of air in these sac-tracheae are effected in a very simple manner. To the outer wall of the sac a broad, and strong ligament is attached; this ligament ascends across the abdomen, and is fixed to the walls of the heart. Each movement of this organ, diastole or systole, strains or slackens the ligament, which in its turn raises or lowers the tracheal sac, and by these means the air is either drawn into or expressed from it (E. Simon, l.c., after E. Blanchard). t. ^ '.

According to Treviranus, l.c. (vz<7β Jones, Anim. Kingdom, p. 416), who, however, makes them four pairs on each side, there are, in the Araneidea, four pairs of spiracles (four on each side of the cephalo-thorax) situated immediately above the insertions of the legs. He also notes four stigmata (in two pairs) on the upper Bide of the abdomen, and a pair on the under side; the former undoubtedly exist, in some species at least, but the latter appear to be imperforate, and are probably only points of muscular attachment. It does not appear that the tracheae leading from the thoracic spiracles have ever been traced; they are, perhaps, exceedingly delicate in their walls, and probably of no great length, and hence after death, when the air has left them, they would be exceedingly difficult to detect. There remains much, doubtless, to be yet discovered in regard to these and other minute details of the internal organisation of spiders.

The Nervous System.— In the order A caridea, as it has been above observed, the nervous matter is concentrated into one large mass or ganglion, whence it branches out to the rest of the body. In the Pycnogonidca the nervous system consists of a longitudinal series of large ganglia, of which the four abdominal ones are sessile. In the Scorpionides, also, it consists of a longitudinal series of eight ganglia distributed throughout the whole body, and united by a triple nervous chord; and now in the Araneidea (as in the Solpugidea, Thelyphonidea (Phrynides), and indeed in the Phalangidea also), we seem to have a compound of these two modifications. Thus, in the Araneidea the nervous matter is, in general, concentrated into two masses, one placed within the fore part of the cephalo-thorax, just above the oesophagus; this (the cephalic or so-called cerebral) ganglion sends out fine nervous threads to the eyes, falces, and labium; the other mass (thoracic ganglion) is situated just behind the former, and occupies a large portion of the thoracic cavity; it is of a flattened disc shape, and is united to the cephalic ganglion by short but broad connectors, forming a narrow collar round the oesophagus. This thoracic ganglion is formed by an approximation and soldering together of the different ganglia which exist separately in the scorpions. A proof of this is furnished by the fact, that in the young of some of the Araneidea, furrows of greater or less depth show the junctional points of the different ganglia.

From the thoracic ganglion lateral nerves issue to the legs and palpi; besides which a fascia of nerves runs backwards through the pedicle into the abdomen, and these subdividing, branch out to all its different organs (Simon, l.c.) A modification of the above exists in the Theraphosides, where there is a special enlargement, or ganglion, just within the fore part of the abdomen, before the nervous fascia subdivides and branches oiιt into that part of the body; probably this modification would be met with also in many other spiders (Cuvier’s An. Kingdom, pl. 2, Arachnides; and Treviranus, l.c., pl. 5, fig. 45).

The Organs of Reproduction in the female consist of two long ovaria placed longitudinally within the ventral surface of the abdomen; these unite and form a short broad oviduct, having aD external opening of various form beneath the upper end of the abdomen between the spiracular orifices, as before noted under the head of external structure.

In the male the organs for the secretion of the seminal fluid consist of two long narrow convoluted tubes, occupying the same relative situation as the ovaria in the female, and also opening outwardly through a common but exceedingly minute orifice in a similar position. No intromittent organ has been discovered in any instance; and it is not long since that the probable way in which the impregnation of the female takes place (at least in some cases) has been at all certainly noted. It has been before remarked that the peculiar corneous lobes and spiny processes connected with the digital joint of the palpi—palpal organs —in the male, are used in the course of copulation; but araneologists were not (and probably are not now) agreed as to their real office in generation. A distinguished author, Mr John Blackwall, went so far as to prove, as he believed, by a series of carefully conducted experiments, that the seminal organs of the male spider, above described, are in some cases wholly unnecessary for the impregnation of the female—at least so far as any external use or application is concerned—and that the palpal organs are the efficient agents in the impregnation of the female spider (Report of Brit. Assoc. 1844, pp. 68, 69). This, however, seemed to be contrary to all reason and analogy, and led to the hypothesis that there was some communication by a duct or ducts between the spermatic vessels in the abdomen and the palpal organs (Hermann, 1868; Verhandlung d. Zool. Bot. Gesellsch. in JVicn, xviii. pp. 923, et seq.) This idea, however, appeared to be negatived by the failure of Dugès and other eminent anatomists to discover any duct in the palpus, where, if present, it would be comparatively easy to find. Another hypothesis— grounded on the fact that the palpal organs have in some cases been observed to be applied repeatedly to the mouth between their numerous applications to the vulva—was, that there might be some duct through which the spermatic fluid could pass into the alimentary canal, and so be conveyed to the oesophagus, and thus be taken from the mouth by means of the above-mentioned application to it of the palpi. The discharge of the spermatic fluid in birds into the lower intestine appeared to support the possibility of this hypothesis being true (O. P. Cambridge, Trans. N. Z. Instit., vol. vi. 1873, p. 190). Another opinion, long since, and even now, held by some arachnologists, is that the male spider collects the seminal fluid with its palpal organs into the concavity of the digital joint from the minute orifice above noted; but no instance has ever been noticed in which a spider has been detected in such an employment of its palpi. An instance has been recorded in which there were during copulation (?) repeated embraces, and at each embrace a perfect apparent coition was effected between the sexual apertures of the male and female spider, the palpi not being used at all (0. P. Cambridge, l.c., p. 191). Other arachnologists, again, have recently observed that the male spider before the act of copulation “emits from the sexual aperture a drop of sperma on a kind of small web made for the puιpose, which drop he then takes up in the genital bulb of the palpi” (A. Menge, Ueber die Lebensw. d. Arachn. p. 36; and A. Äusserer, Beob. ueber die Lebensw. der Spinnen, p. 194). This would appear to settle the question; but while, at the same time, it is remarkable that an observer so accurate in observation and so painstaking as Mr Blackwall should never have observed male spiders taking the spermatic fluid from the abdominal aperture, as stated by Menge some thirty years ago, it is also remarkable that Mr Blackwall should unconsciously afford the strongest evidence in favour of the facts mentioned by Menge and Äusserer.

Dugès, in suggesting, long since, that the male spider took the seminal fluid from the aperture in the abdomen with its palpi, asked whether the palpal organs may not alternately act as an absorbing siphon and an ejaculatory organ. Mr Blackwall (Jour. Linn. Soc. , vii.) mentions this question of Dugès, and then states a fact which at once answers the first part of it in the affirmative, and tends to confirm Menge’s and Ausserer’s statement: “A male Agelena labyrinthica confined in a phial, spun a small web, and among the lines of which it was composed I perceived that a drop of white milk-like fluid was suspended; how it had been deposited there I cannot explain, but I observed that the spider, by the alternate application of its palpal organs, speedily imbibed the whole of it.”

That the spermatic fluid is conveyed to the female parts of generation by the male palpi is thus pretty certain; and it seems not improbable that there are more modes than one by which the palpi are supplied with the fluid. See also critical observations on this subject by Dr. T. Thorell, 1873, Synonyms of Europ. Spid. pp. 591- 595.

Before concluding our remarks on the internal structure of the Araneidea, two of their special properties must be shortly noticed—the secretion of the poison injected into the wounds made by the fangs of the falces, and the secretion of the matter emitted as silken threads through the spinning organs.

The poison is secreted in two small elongated sacs (one for each of the falces), situated within the cephalothorax on either side of the alimentary canal; the sacs are connected with a membranous channel in each of the falces, the channel running completely through the fang, from an orifice near the end of which the poison is pressed out by the spider in the act of wounding its prey. On the venomous nature of the poison some remarks have already been made. As to its venom in British spiders, see “Blackwall’s Experiments,” Trans. Linn. Soc., xxi. pp. 31-37. The result of these interesting experiments is contrary to the generally received idea as to the great virulence of spider poison.

The external spinning organs have been mentioned above; they are usually called spinners, and are various in size, both actual and relative, in form and in structure, as well as in number. From the extremity of each of these organs the silk matter issues through numerous movable papilla, or spinnerets, which are similar to hollow bristles with enlarged bases; the papillae vary both in form and number in different species, and from each spinneret or papilla issues an exceedingly fine thread; this, uniting with threads from all the other papillae, forms the ordinary silk line, which though to ordinary observation simple, is composed of numberless threads from some one, or all, of the spinners. The matter from which the silk is formed is secreted in organs (silk-glands) situated within the ventral surface of the hinder part of the abdomen. These glands vary in number, size, and form in different species; they differ also in size and shape in the same species, for the secretion of different qualities of silk-matter; and each gland has a distinct duct terminating at the extremity of the spinners. The emission of silk matter appears certainly to be a voluntary act on the part of the spider; but it is a disputed question among arachnologists, whether spiders have the power forcibly to expel it, or whether it is merely drawn from the spinnerets by some external force or other. Mr Blackwall (Trans. Linn. Soc., xv. p. 455; Researches in Zoology, pp. 242-248, and History of Spiders of Great Britain and Ireland, p. 12) is of the latter opinion; while Mr R. H. Meade (of Bradford, Yorkshire), in Report of British Assoc., 1858, pp. 157-164, pl. 16, thinks that (from microscopic anatomical investigations which he has himself made) there is good evidence of spiders having the power to expel it, for he finds a certain muscular arrangement which would apparently suffice to give this power, and observers have actually seen the lines propelled. Mr Meade, however, need not be assumed to assert an indefinite power to expel threads of silk to any indefinite distance. The truth probably is, that spiders have, and do exercise, a general power not only of emitting silk matter from the secreting glands merely to and from the external orifices of the silktubes, but also of propelling it when necessary to some short distances; and that external causes (such as the movement of the spider while the end of its line is fixed, or when a current of air takes an emitted line and carries it in a direction contrary to that of the spider) also serve to draw the threads out. In all these ways, no doubt, are produced the gossamer lines which often cover the surface of the ground and herbage in autumn. In the formation of their snares spiders use the hinder or fourth pair of legs for drawing the threads tight, and apparently for ascertaining their power of tension. The third, or inferior tarsal claw, being usually strongly bent, no doubt enables spiders to perform these operations very readily. Some large groups of spiders do not spin any snares, and in them we usually find this third claw absent; while in one group, Epeïrides, whose snares are marvels of beauty and ingenuity, the third claw is very highly developed.

The snares of spiders have been made the basis of some of the primary divisions of the order. Characters, however, taken merely from habits and modes of life, can hardly be considered those on which systematic classification should be based, not to mention that those characters fail when we come to extensive groups spinning no snares at all. Short of such a use of the snares of spiders, this part of the subject is of extreme interest and importance. The Latreillian divisions of snares is fairly and generally accurate; by this method they are divided into— Orbitelarioe, where the plan is that of a circle or a portion of one, with lines radiating from a centre; Retitelarioe, where a thin sheet of web is suspended among the branches of shrubs or in angles of buildings, and held up and down by lines in all directions above and below; Tubitelarioe, where the snare is a silken tube, inserted in crevices, and fissures, and casual holes, and with an open mouth more or less guarded or armed with insidious lines; and Territelariae, in which a tube is spun in a hole formed by the spider itself, and closed sometimes by a close fitting cork-like, or sometimes by a scale-like or wafer lid, sometimes left open, and at other times closed by the falling over of a portion of the tube which protrudes from the surface of the ground (see Trapdoor Spiders, by J. T. Moggridge, Lovell Reeve, London, 1873-4). With respect to the economic or mercantile value of spider silk, the idea seems to have been entertained, from a remote period, that it might not only be turned to practical use in the manufacture of silk fabrics, but also be made to pay as a mercantile speculation. The possibility of making it into articles of wear is undoubted, as instances of it are on record. Upwards of 150 years ago Le Bon of France (Languedoc) obtained, from spiders, silk which was afterwards woven into gloves and stockings; but Réaumur, appointed by the French Academy to investigate the matter, reported unfavourably, doubting the possibility of rearing the spiders together owing to their voracious and cannibal propensities. In 1777 and 1778 a Spaniard, Raimondo Maria de Termeyer, published, in Italian periodicals, two memoirs on the subject; and afterwards, 1810, at Milan, another called Ricerche e Sperimenti sulla Seta de Ragne, in which he takes an opposite view to that of Réaumur. The latter work is of great rarity (vide B. G. Wilder in Harper’s New Monthly Mag., xxxiv. p. 455). Termeyer constructed a small kind of stocks, in which the spider was fixed by the body, while with a little winding-machine he drew out and wound up the silk threads from the spider’s spinnerets; but evidently nothing came of this further than an additional proof of the possibility of procuring and making use of spider silk, as well as of its strength and lustre; this last, however, as well as other qualities of the silk, would probably be found, as with that of various silk worms, to vary according to the species. Other experiments, with a similar general result, have been made since (Zoologist, 1857, p. 5835), the latest being those made by Dr B. G. Wilder, professor of anatomy in the Cornell University at Ithaca, United States (l.c., supra), with Nephila plumipes (Koch), a large epeïrid abundant in South Carolina. His experiments appear to have been unconsciously, though surprisingly, similar, and with a similar result, to those of Termeyer; but the question as to the mercantile importance of spiders’ silk appears to have hitherto elicited only an unfavourable answer. Dr Wilder, however, is still sanguine upon the point (vide B. G. Wilder, l.c., and also in Proc. Boston. N. H. Soc., October 1865, with other references there noted, as well as in The Galaxy, July 1869, pp. 101, 112). In Zoologist, 1858, p. 5922, a correspondent, speaking of the strength of the silk threads of Nephila clavipes, says that small birds are sometimes entangled in its webs, and that the ladies of Bermuda use the threads for sewing purposes. See also Phil. Trans. 1668.

Before leaving this part of the subject, we must notice the office of the calamistrum, mentioned before in speaking of the armature of the legs of spiders. This instrument is found in the females of various genera and families; it consists usually of a closely set double row of curved spine-like bristles on the upper sides of the metatarsi of the fourth pair of legs, forming a kind of comb, whence Mr Blackwall, by whom it was first discovered and its use perceived, gave it the name it bears. Its office is to card, or curl, or tease a particular kind of silk emitted from the supernumerary spinners, mentioned above as always, in the female, correlated with this instrument; the silk so curled and carded is, owing to the fineness of its fibres, exceedingly prehensile, and being disposed about the lines of the spider’s snare, serves to entangle the insects which come in contact with it (vide Blackwall, Linn. Trans., vol. xvi. p. 471, pl. 31, 1831). Amaurobius similis (Bl.) and A. ferox (Koch) are common house spiders whose webs are thus furnished with carded silk from the supernumerary spinners. Doubts have been entertained quite lately by an eminent araneologist as to whether the supernumerary spinners are indeed true spinning organs (T. Thorell, Synonyms of European Spiders, p. 595, 1873). It is therefore interesting to find in Science Gossip (Hard-wicke, London, Sept. 1874), a short article by H. J. Underhill, in which the anatomy of these spinners is described and figured from original microscopic investigations, proving the recorded observations of Mr Blackwall, and others also, as to their being true spinners, to be correct.

The white flake-like flocculi often seen floating in the air on a calm autumnal afternoon are composed of spider silk emitted by numerous immature spiders, of many species and genera, passing through the air on their lines, which being so much lighter than the atmosphere, serve to bear them away with every breath of wind. The flocculi appear to be agglomérations of fine lines, adhesive from their fineness and fibrous nature. In this respect they differ from the ordinary gossamer lines, which are merely the threads left by small and immature spiders (chiefly of one or two families,) as they pass from blade to blade and plant to plant. It seems probable that nearly all spiders leave a line or lines, which proceed from one or more of their spinners, whenever and wherever they move about; and the setting in of fine weather being the signal for a spontaneous restlessness, we can hence better understand the almost sudden appearance of myriads of lines stretching over the surface of the earth, and often extending high up into the air. Numerous papers have been written on gossamer, chiefly by German and French writers, with the latter of whom the subject has been sometimes treated on the basis of the marvellous and superstitious. These lines are called by them fils de la Vierge.

Our space does not permit of any great detail respecting the various kinds of snares, nor regarding the way in which different spiders construct them. Accounts may be found, by Mr Blackwall, in Zool. Journ. 1830, pp. 181-189; as well as in the Report of the British Association for the Advancement of Science for 1844, pp. 77-79; Researches in Zoology, 1st ed. 1834, pp. 253-284; Linn. Trans. 1831, pp. 471-479; and A History of the Spiders of Great Britain and Ireland, 1861-64, all by the same author; and the exceedingly interesting details on this subject in Kirby and Spence’s Entomology, pp. 227-267 (7th ed.), are within every one’s reach. The following notes, however, gathered from the works of Mr Blackwall and others, as well as from the writer’s own observations, may be of interest :—

The geometric spiders (Orbitélarioe) are almost the only ones whose method of forming a snare have been at all minutely recorded. When the situation for the snare has been chosen, the area intended to be filled up by it is enclosed by various circumferential boundary lines, fixed to adjacent objects, the exact shape of the area being influenced by the situation and surrounding circumstances. A diagonal thread is then spun across it, and from about the central point of this thread another is carried to the marginal line; returning to the central point along the line just spun from it, the spider carries another line to the margin, and fixes it at a short distance from the first. In this way the whole area is gradually filled up, the spider always returning to the centre along the last line spun, and starting again thence fixes a fresh one to the boundary line of the snare. The form of the snare is now that of a wheel; the next operation is to cross the radii of the wheel with ladder-like lines; this the spider does, beginning from the centre and working towards the circumference, with a single spiral line, which is fixed, or glued, with a minute portion of viscid matter, to each of the radii as it crosses by an application of the spinners; at some distance from the centre this spiral line is discontinued and another is begun; this is formed of quite a different kind of silk matter, being viscid, and retaining its viscidity in the form of “minute dew-like globules closely studding the line.” It appears that when the viscid lines, intended for the capture of its prey, are completed, the spider cuts away the first, or unadhesive line, which is of no service in the entanglement of insects, its office appearing to be chiefly to strengthen the snare while the viscid line is being spun, and to enable the spider to traverse the parts with greater ease. Modifications of the above method are, no doubt, adopted by some species, but, substantially, it is believed that most orbicular snares are thus constructed.

The mode of formation of the snares of the Retitelariae does not appear to have been observed, probably owing to their being made almost wholly during the night. The snare of one of these spiders, Linyphia marginata (BL), is an exceedingly perfect one of its kind, and abundant in most localities; it consists of a thin horizontal sheet of web, suspended among the branches of low evergreen trees and shrubs, by a maze of intersecting lines above, and held down firmly, on the under side, by some short, tightly-strained perpendicular lines, fixed below to others, which traverse each other in all directions; beneath the horizontal sheet of web, head downwards, the spider remains patiently watching for such insects as may become entangled in the upper maze of lines. The mode in which the horizontal web is suspended and braced down, would, without doubt, if it could be observed, prove to be a point of great interest.

Among the Tubitelarioe we have the observations of Mr Blackwall, directed chiefly to the formation by Amaurobius atrox of the peculiar fibrous and adhesive flocculus, drawn from the fourth pair of spinners by the “calamistrum,” and disposed about the irregularly intersecting lines of the snare which is spun in the angles of walls, in crevices, between portions of detached rock, and other similar situations. The adhesive flocculus serves to entangle insects, and makes them an easy prey to the spider who lies in wait not far off, having formed a funnel-shaped tube of slight texture from its place of concealment to its snare.

With regard to the formation of the snares of the Territelarioe, Mr Gosse has an interesting passage in A Naturalist’s Sojourn in Jamaica; it is, however, too long for quotation here. Mr Moggridge also (l.c. infra} has some details respecting the formation and repair of their neste by trapdoor spiders in confinement. The chief point of interest, however, in regard to trapdoor snares, is whether the hinged lid is formed in one continuous piece with the tube, and then cut out, leaving a portion unsevered to form the hinge, or whether the lid is made separately, except in that part intended for the hinge. Neither Mr Gosse nor Mr Moggridge enter into this question, though Mr Moggridge indeed speaks (Z.c, p. 118) of his belief that, when all is completed, the spider cuts away certain threads by which the door is supported on either side of the hinge. The present writer was once told by a gentleman who had formerly resided in the West Indies, that trapdoor spiders there invariably make the tube and lid of one continuous, solid, homogeneous piece, and then cut out the lid with the falces. This account, especially as coming from a non-naturalist, seemed improbable—a spider’s falces being in no way, apparently, fitted for such an operation; if, however, the fact be that the lid, instead of being of one solid piece with the tube, is merely connected with it by a few supporting threads (in accordance with Mr Moggridge’s belief), these could easily be torn away by the spider’s falces, and the lid would be left free, except at the point where the hinge is formed.

Classification. —It is impossible within our remaining space to go into detail upon this wide portion of the subject; it must suffice to say that the order Araneidea may at present be divided into about thirty - two families. These are — Theraphosides, Colophonides, Filistatides, Oecobiïdes, Tetrablemmides, Dysderides, Drassides, Γalpimanides, Dictynides, Agelenides, Hersilides, Scytodides, Γhotcides, Theridiides, Phoroncιdides, Epeιrides, Gasteracanthides, Uloborides, Miagrammopides, Poltides, Thlaosomides, Arcydes, Stephanopides, Eripides, Thomisides, Podophthalmides, Lycosides, Sphasides, Dinopides, Salticides, Myrmecides, Aphantochilides. In these families are comprised about two hundred and sixty genera based upon special details of structure; principally the position of the eyes, the form of the maxillae and labium, the number and structure of the spinners, and some other details. The species are very numerous; probably not a tithe of the existing ones are yet described. In one family alone, Salticides, nearly a thousand are known.

As in all other creatures, differences of colour and markings, as well as integumental clothing and armature, serve to distinguish the species—the latter, too, are at times of generic value; but with regard to spiders particularly, in order to determine their species, it is very essential to obtain comparative dimensions from different portions of structure; thus the position of the eyes on the fore part of the caput furnishes us with the facial space (or the space between the margin of the caput just above the falces and the posterior eyes nearest to the medial line), and the clypeus, or the space between the same (fore) margin of the caput and the anterior eyes nearest to the medial line. The comparative extent of these parts is of great importance as specific characters, and they are easily observed; that part of the facial space occupied by the eyes is concisely described as “the ocular area." The relative and comparative lengths, again, of the legs, and of their different joints, are strong specific characters, the first also generic. Male spiders when adult may, with few exceptions, be certainly distinguished in regard to their species, by the form and structure of the palpi and palpal organs, the development of the latter being an infallible criterion of maturity. Female spiders, again, may, in numerous cases, be as certainly distinguished by the form and structure of the genital aperture, situated in the medial line beneath the fore extremity of the abdomen; this aperture is never externally “perforate” until the last moult of the spider, and its full development is therefore an unerring criterion of the maturity of the female sex. With respect to the senses of spiders—smell and hearing—nothing appears to have been certainly ascertained; but the late Mr Richard Beck has an interesting paper upon the subject in Entomologist, Lond. 1866, vol. iii. p. 246. He suggests that the fine and delicate hairs of some spiders’ legs may convey sounds to them. With regard to the sense of taste we may well conclude that spiders have this sense in considerable perfection, in the possession of a well-developed membranous tongue.

General Remarks. —Spiders are to be found more or less abundantly in every part of the world and in almost every conceivable position; even subterranean caves, such as those of Adelsberg and the Island of Lesina, are tenanted by species peculiarly adapted by the absence of eyes to their dark and gloomy abodes. Less repulsive and forbidding in appearance than most others of the Arachnida, the Araneidea are often extremely interesting in their habits. Being almost exclusively feeders on the insect tribes, they are consequently endowed with proportionate craftiness and skill; this is shown remarkably in the construction of their snares and dwellings. The “trapdoor spider” has always been one of note in popular works on spiders’ habits, and certainly the details of several different types of the trapdoor tubular nest, with the habits of the several species to which they belong, lately published by Mr Traherne Moggridge, are of the greatest interest and importance. The typical trapdoor nest is a cylindrical hole in the earth excavated by the spider itself, lined with silk and closed by a lid, which fits like a valve or cork into the opening at the surface and opening by a strong elastic silken hinge, the spring of which closes it again with some slight force. Many spiders, however, live a vagabond life, and capture their prey without the aid of a snare, by springing on it unaw ares, or, in some cases, running it fairly down in open view; yet craft and skill are equally apparent, whatever be their mode of life and subsistence.

To say that spiders are less repulsive and forbidding in appearance than other Arachnids, is to do them but scanty justice, for numbers of species of various genera—notably among the Salticides, or jumping spiders—are unsurpassed by insects of any order, in respect both to brilliancy of colouring and the designs formed by its distribution. Some of the curious and delicate little species of the genera Argyrodes and Ariamnes are perfect marvels of metallic brilliancy and beauty. These little spiders are found living as quasi parasites, in the outskirts of the webs of the larger exotic epeïrids, and appear to live on the smaller insects caught in them; probably also spinning irregular snares of their own among the lines of the larger snare. In external appearance the young of spiders do not differ greatly from the adults, except in being generally more distinct in colour and markings; in some species the characteristic markings can seldom be w ell traced except in immature examples. The cocoons or nests in which some spiders deposit their eggs are very beautiful, as w ell as varied and characteristic in form; that of Ero variegata (Bl.), a little spider not uncommon in England, w ould arrest the attention of even an indifferent person; it is of an elegant pear shape, formed of a strong yellow-brown silk network, and attached by a long elastic stem, of the same material, to stalks of dead grass, sticks, or other substances, in shady places. Another, made by a larger spider, Agro'éca brunnea (Bl.), is of a truncated pear shape, formed of a continuous white silk fabric, and attached to blades and stalks of living grass and rushes, by a short pedicle; it must, however, be seen soon after it is made, for the maker, as if prescient of the attraction of such a beautiful little object, hastens to daub it over thickly with a coat of mud or clay, which completely conceals its structure and beauty.

Spiders vary greatly in their relative fertility; probably many species are rare owing to a limited fecundity. The egg sac of Agroëca brunnea (Bl.) contains about forty or fifty eggs, that of Xysticus claveatus (Walck.) about twenty, that of Ero variegata (Bl.) not so many, while that of Oonops pulcher (Tempi.) contains usually no more than two. Some spiders, however, perhaps most, construct more than one cocoon.

From their mode of life spiders attain (as we should naturally suppose) their largest size, and are found in their greatest profusion, in the tropical regions; while in more temperate climates, where the members of the insect tribes are smaller and their species fewer, we find spiders in general of comparatively smaller dimensions and less numerous in species. One of the largest known spiders, Eurypelma Klugii (Koch),—Fam. Theraphosides—found in Brazil, measures upwards of two and a half inches in length, with legs nine inches and upwards in span; while the smallest known spider, Walckenaëra diceros (Cambr.), found in England, is but -⅛th of an inch in length. Tropical countries, however, although some of their spiders are giants, have numbers of small size. Numerous species have been procured from Ceylon measuring no more than from ∙⅛th to - j 1 -θth of an inch in length.

Spiders, besides being skilful and crafty, are very cleanly; one of our common Saltici, Epiblema histrionica (Koch), may often be seen brushing and cleaning its forehead and eyes with its hairy palpi, as a cat uses its paws for a similar purpose. Probably most spiders, like the Crustacea, have the faculty of reproducing a lost limb. Instances of this are numerous (see Mr Blackwall’s experiments, Report of British Association before cited), but a reproduced limb is seldom or never equal to the original one in size; this accounts for the frequency of examples captured with one or more legs, or a palpus, of dwarfed and stunted dimensions. Many spiders show great attachment to their eggs and young. The female Lycosa will seize her egg sac again and again if it be taken from her, only relinquishing it at last when apparently convinced of the hopelessness of retaining it. A pretty little spider, not rare among weeds and garden plants, Theridion carolinum (Walck.), carries its egg cocoon within its legs, and searches for it anxiously if compelled to drop it. Many also of the genus Clubiona, as well as others, brood over their eggs and tend upon their young until they disperse to find their own means of subsistence. The food of very young spiders is probably wholly derived from the moisture of the atmosphere. Spiders are great drinkers, and suffer severely from drought. Mr Blackwall relates that an emaciated, half-dead example of Micaria nitens (BL) grew immediately plump and strong after a draught of water.

In speaking of the better qualities of spiders, their attachment to their young, and the frequent fondness for each other evidenced by the apparently happy life of the male and female of some species in the same web, we must not overlook the other side of the picture. It has been well authenticated that in some species of Epeïrides the female will seize and devour the male even immediately after the exercise of his natural office, which indeed he has to undertake with great circumspection and care to be able to accomplish at all. From this propensity of the female, we may account for the gradual lessening in size of some male spiders in comparison with that of the females, by a kind of sexual selection, since it is obvious that the smaller the male the better his chance of escape (see O. P. Cambridge in Zoologist, 1868, p. 216, and in Pro ceedings Zool. Soc. Bond., 1871, p. 621, and also Vinson’s Spiders of Bourbon and Mauritius'), and thus selection would operate until the males became so small as only just to be able to fulfil the office of impregnating the female. The male, nearly always the smallest, is in the case of some epeïrids and Thomisids not τ ⅛th or even τ ⅛th of the length of the female, and sometimes not more than τ ∕ δ - δ ∙th part of her weight, and less then τ √ 5 - 5 ∙th part of her volume (A. W. Μ. Van Ξasselt, Arch. Neerland, tom. viii.) As a rule, however, the difference in size between the male and female spider is not nearly so great. Spiders are unable to fly, and the mode adopted by many species, and myriads of individuals, to make up for this by sailing away on their silken lines, has been mentioned; but lately a beautiful species of Salticides, Attus volans (Cambr.), Ann. and Mag. N. H., September 1874, found at Sydney, N.S.W., has been described and figured, with large flaps or lateral extensions of the abdominal integument, by means of which the spider can sustain itself in leaping from plant to plant; it has power to elevate and depress these flaps at will.

The voracity of spiders is well known, and the propensity above noticed of the female to devour the male is but one instance of general voracity; but though thus voracious, spiders can endure extreme fasting with impunity. A small spider enclosed in a glazed case, lived and appeared healthy for eighteen months without food; if it had any nourishment at all during this time, it could only have been the very slight moisture that might exude from the skin of a lately stuffed bird in the case, Zoologist, 1853, p. 3766. Other instances are also on record of fasts, almost or quite as long, and borne equally well.

Enemies of Spiders. —Preying upon all the insect tribes, and occasionally upon lizards (F. Pollock, Ann. N. H., October 1872) and earth-worms (E. Simon in Ann. Soc. Ent. Erance, 1873, 5 sér. tom. iii. p. 114—and Zoologist, 1856, p. 5021), spiders are also themselves preyed upon by both lizards and insects. More than one species of parasitic hymenoptera tend to keep spiders within due bounds; but little has yet been done towards working out these parasites. Three species are figured in Blackwall’s Spid. Great Britain and Ireland, pl. xii.; two of them prey upon Agroëca brunnea (Bl.); while the third, Pompilus sepicola (F. Smith), pierces large spiders, paralysing, but not killing them; they are then dragged to its nest, in a hole in the earth; eggs are laid in the spider, which retains sufficient vitality to furnish fresh food to the parasitic larvae until the time for their change to the pupa state arrives. Full grown females of Lycosa campestris (Bl.) have been found by the writer in the grasp of this powerful ichneumon. From the outskirts of a single web of Epèira opuntioe (Buf.), on the shores of the Sea of Galilee, the writer collected, in April 1865, many truncated pear-shaped egg cocoons belonging to the beautiful little Argyrodes epéirae (Sim.); and from each of these cocoons a single hymenopterous parasite shortly issued. The egg cocoons of various epeïrids in England are likewise often preyed upon by numerous minute parasites of the same order. Several species of Theridion—T. simile (Koch) especially —are subject to a larval parasite, often as large as the spider itself, adhering to the outside of the abdomen. Various attempts to rear the perfect insect from this para-· site have hitherto failed. A wide field of great interest is open to any one who should take up the investigation of the various insect parasites of spiders, with their mode of attack and subsequent victory.

Other foes, common to all the Articulata, spiders also have in abundance—birds, small mammals, and reptiles. Doubtless we are indebted to such enemies for the development, through natural selection, of many spiders protected by horny integuments, and often armed with spines to an extent that would make them a painful meal to any bird or other creature that should set itself to dine upon them. Phoroncidia Thwaitesii (Cambr.), found in Ceylon, and Pycnacantha Meadii (Bl.), found in Africa, and indeed all the Gasteracanthides, are notable examples of this protective armature. Protective ‘ ‘ mimicry’’ is also seen in spiders, some so exactly resembling ants, that placed side by side with species of ants found in the same localities, even a practised eye would not detect the spider at first sight Of this nature are the Myrmecida (fig. 31) and some of the Saltici, and, notably, Aphantochilus Pogersii (Cambr.), found in Brazil. Other spiders, again (Genus Eurysoma, Koch, and Cyrtarachne Thor.), closely resemble some species of phytophagous coleoptera; one of the latter genus found in Ceylon, but yet undescribed, resembles a small mollusc. Of the former some are very like a minute crab (fig. 32). And lastly, to sum up the enemies of spiders, they prey on each other, and are preyed upon also by other Arachnids; but on the whole they have, as by their office they should have, the best of it, for they are against all the Articulata, but only comparatively a few of the Articulata are against them.

Spiders are not creatures which belong solely to the present geologic era of the earth, for fossil spiders, with other Arachnids, as well as spiders in amber, have been found; the oldest in the coal formation. See on this subject a late résumé by Dr T. Thorell, On European Spiders, pp. 220- 233, with other works there quoted.

Preservation of Spiders. —Beautiful as are the colours and markings of numbers of spiders, especially of those found in the tropics, and elegant and curious as are many of their forms and structures, it has yet been found a matter of difficulty to make them good-looking, sightly, cabinet objects. By ordinary care and skilful manipulation, however, most of them can be preserved and displayed very satisfactorily. So much of the comparative neglect of Arachnids in general is owing to this difficulty, that it may perhaps be worth the space of a few lines to remark, that many whose abdominal integument is strong, or pretty thickly clothed with hairs and pubescence, may be pinned, set out, and dried like insects. · Others may have the abdomen opened from below, and after the contents are carefully extracted, be stuffed with fine cotton wool. Others again have been most successfully treated by inflating the abdomen (after the contents have been pressed out) with a blow-pipe, and then subjecting them to a process of rapid desiccation, which in general preserves the colours and markings very well indeed. But the best and most useful way for all purposes is to immerse and keep them in tubes filled with spirit of wine. To make spiders in spirit sightly objects, they should, when drugged with chloroform, or some other stupifying agent, be secured, but not transfixed, by pins to a piece of cork, sunk in a vessel of spirit, in a natural position, until rendered rigid by the action of the spirit, which will be in a fortnight or so; the pins are then removed, and the spiders are placed in glass test tubes, large enough to receive them without too much compression of the legs. A bit of white card is slipped in under the specimen to keep it in position, the tubes are filled with spirit, stopped firmly with a pledget of cotton wool, and inverted round the inner side of a wide mouthed glass-stoppered bottle; this bottle is filled also with spirit, and the spider is then seen in its natural position, and with all its colours and markings perfectly visible. It is also capable of examination with an ordinary pocket lens, even without removal of the tube from the large bottle. Large spiders with a largely developed abdomen should be kept in pill-boxes for a fortnight or so before being placed in spirit; during this time the crudities of their food contents are discharged, and preservation without injury or obliteration of colours and markings is thus rendered far more certain; the beauty of many of our large and handsome epeïrids can only be certainly retained, even in spirit, when treated after the above method. See further on this subject, as well as on the mode of search and capture of spiders (O. P. Cambridge, Trans. Neu Zeal. Instil., vol. vi. pp. 194-200).

It is not necessary to give here a list of works on Arachnids, many having been already quoted in speaking of the different orders. The following, however, on Ara-neidea raay be mentioned :—

N. Westring, ti Araneae suedcae,' Gothenburg, 1861; E. Ohlert, Die Araneiden oder Echten Spinnen der Provinz Preussen, Leipzig, 1867; A. Menge, “l’reussiche Spinnen,” in Sehr. Ges. Danz. (N. F.), 1866-1873, Danzig (still in course of publication); H. Lucas, in Exploration de l’Algérie, Paris, 1849; H. Nicolet, in Gay’s Hist. Fis. Pol. de Chili, vols. iii. iv., Paris, 1847; Eugène Simon, Les Arachnides de France (vol. i. only is yet published), Paris, 1874; L. Koch, Die Arachniden Australiens, Nuremberg, 1871-74 (still in continuation). Nothing has been said in the foregoing pages respecting the “Embryology” of spiders; for information in regard to this important and interesting but recondite part of Araneology, it must suffice to refer the reader to Herold, De Generatione Aranearum in Ονο, Marburg, 1824, and Edouard Claparède, Recherches sur revolution des Araignées, Utrecht, 1862.

These, with other works quoted on the different points that have arisen in the course of the foregoing article, will be found sufficient to guide the student and collector. The general works on Arachnida, or on any of its separate orders, are exceedingly few, and none, except that of Μ. Simon, Hist, des Araignées, Paris, 1864, are of recent date, beyond the merest abstracts. The literature on the subject is scattered up and down, in isolated papers, in numberless Transactions and Proceedings of various societies, and in scores of periodical volumes and journals for the record of natural and scientific investigation. It has been attempted to give in the foregoing pages as fair a general view of the whole subject as the limited space, and great difficulty of getting access to important papers treating upon it, would permit. The object of such articles as the present is rather to excite an appetite for the obtaining more detailed information, than to satisfy fully the appetite already excited. (o. P. c.)