In 1816, De Blainville, adopting Latreille’s view, divided the Linnaean Amphibia into Squamiféres and Nudipelliféres, or Amphibiens; though he offered an alternative arrangement, in which the class Reptiles is preserved and divided into two sub-classes, the Ornithoides and the Ickthyoides. The latter are Brongniart’s Batrachia, plus the Coecilioe, whose true affinities had, in the meanwhile, been shown by Duméril; and, in this arrangement, the name Amphibiens is restricted to Proteus and Siren.

Merrem’s Pholidota and Batrachia (1820), Leuckart’s Monopmoa and Dipnoa (1821), Miiller’s Squamata and Nuda (1832), are merely new names for De Blainville’s Ornithoides and Ichthyoides, though Müller gave far better anatomical characters of the two groups than had previously been put forward. Moreover, following the indications already given by Von Bär in 1828, Müller calls the attention of naturalists to the important fact, that while all the Squamata possess an amnion and an allantois, these structures are absent in the embryos of all the Nuda.

Müller makes an appeal for observations on the development of the Coecilioe, and of those Amphibia which retain gills or gill-clefts throughout life, which has unfortunately yielded no fruits from that time to this.

In 1825, Latreille published a new classification of the Vertebrata ,6 which are primarily divided into Hoematherma, containing the three classes of Mammifera, Monotremata, and Aves ; and Hoemacryma, also containing three classes — Reptilia, Amphibia, and Pisces. This division of the Vertebrata into hot and cold blooded is a curiously retrograde step, only intelligible when we reflect that the excellent entomologist had no real comprehension of vertebrate morphology; but he makes some atonement for the blunder by steadily upholding the class distinctness of the Amphibia. In this he was followed by Dr J. E. Gray; but Duméril and Bibron in their great work, and Dr Günther in his Catalogue, in substance, adopt Brongniart’s arrangement, the Batrachia being simply one of the four orders of the class Reptilia. Professor Huxley has adopted Latreille’s view of the distinctness of the Amphibia, as a class of the Vertebrata, co-ordinate with the Mammalia, Aves, Reptilia, and Pisces; and the same arrangement is accepted by Gegenbaur and Haeckel. In the Hunterian lectures delivered at the Royal College of Surgeons in 1863, Professor Huxley divided the Vertebrata into Mammals, Sauroids, and Ichthyoids, the latter division containing the Amphibia and Pisces. Subsequently he proposed the names of Sauropsida and Ichthy-opsida tor the Sauroids and Ichthyoids respectively. It is proper to mention, finally, that Professor Owen, in his work on The Anatomy of Vertebrates, follows Latreille in dividing the Vertebrata into Hoematotherma and Hoemar tocrya, and adopts Leuckart’s term of Dipnoa for the Amphibia.

The Amphibia are distinguished from the Sauropsida and Mammalia by very important and sharply-defined characters. The visceral arches of the embryo develop gills, which temporarily, or permanently, perform the respiratory function. There is no trace of an amnion, and it is still a question whether the urinary bladder, which all Amphibia possess, answers to the allantois of the higher Vertebrata or not. At any rate, it plays no part in the respiration of the embryo, nor is it an organ by which nutriment is obtained from the parent. There are two occipital condyles, and the basi-occipital region of the skull is either very incompletely, or not at all, ossified. There is no basi-sphenoidal ossification. When young, the Amphibia are provided with, at fewest, three, and usually four, cartilaginous, or more or less ossified, branchial arches. From Pisces, on the other hand, they are distinguishable only by the characters of their locomotive apparatus. When they possess median fins and limbs, these never present fin-rays; and the limbs exhibit, in full development, the type of structure which obtains among the Sauropsida and Mammalia, and differ very widely from the fins of any fish at present known. This difference obtains even among the long extinct Amphibia of the Carboniferous epoch. In other respects, the lower Amphibia approach the Chimoeroe, the Ganoidei, and the Dipnoi very closely; while, in their development, they present curious approximations to the Marsipobranchii.

With respect to the primary subdivisions, or orders, of the class Amphibia, no one can doubt the propriety of the separation of the recent forms into what may be broadly termed Newts (Urodela) ; Frogs and Toads (Anura); and Concilia (Peromela) effected by Duméril; while all that is known of the organisation of the extinct Amphibia of the newer Palaeozoic, and older Mesozoic, formations tends to show that they form a fourth natural assemblage of equal value to each of the others.

The names of Urodela and Anura, given to the first two of these divisions, are undoubtedly open to criticism; but if well-understood terms, which have acquired a definite scientific connotation, are to be changed whenever advancing knowledge renders them etymologically inappropriate, the nomenclature of taxonomy will before long become hopelessly burdened; and, to set a good example, the names of Urodela, Anura, Peromela, and Labyrintho-donta are adopted here for the four orders of the Amphibia, even although it be true that the Labyrinthodonta do not all possess the dental structure on which the name was founded; though there is reason to believe that some Labyrinthodonts were devoid of limbs, or peromelous; that the Anura are not more tail-less than are the Peromela; and that the tails of the Urodela are not more conspicuous than were those of the Labyrinthodonts.

The Urodela, are Amphibia with elongated bodies and relatively short limbs, devoid of scales or pectoral plates, with numerous prae-caudal vertebrae, and with amphicoelous, or opisthocoelous, vertebral centra. The hyoidean arch remains connected with the suspensorium throughout life, and its cornua are large in proportion to its body. The mandible is dentigerous. There are one or two pairs of limbs, the pectoral arch and limbs being always present. The manus never possesses more than four digits. The bones of the antebrachium and of the crus remain distinct, and the tarsus is not elongated. So far as the spermatozoa are known, they are elongated filaments with a vibratile fringe. The larva develops external gills only; and, except Siren, none are known to possess, at any time, a homy masticatory apparatus.

The Anura have relatively short and broad bodies, and both pairs of limbs are constantly present, the hinder being the longer and stronger. There are no scales, nor pectoral plates, but ossification sometimes occurs in the dorsal integument. The vertebrae vary in character, but are usually procoelous. The prae-sacral vertebrae never exceed nine in number, and the caudal portion of the vertebral column is represented by a peculiar styliform coccyx. The hyoidean arch detaches itself from the suspensorium, and almost always becomes connected with the pro-otic region of the skull. The cornua are usually slender, as compared with the broad body of the hyoid. The mandible is almost always devoid of teeth. The bones of the antebrachium and of the crus early ankylose, and the astragalus and calcaneum are much elongated. The manus has a rudimentary fifth digit. Except in Bombinator, the spermatozoa have, flagelliform appendages, like those of ordinary Vertebrata. The larvae develop first external, and afterwards internal, gills, and, so far as is known at present, are provided with deciduous horny masticatory plates. The gill apertures are closed by the growing over them of an opercular membrane.

The Peromela have snake-like bodies, totally devoid of limbs and limb arches. In most, the integument is provided with transverse rows of imbedded cycloid scales, but there are no pectoral plates. The vertebrae of the trunk are very numerous, and are amphicoelous; those of the caudal region are very few, and are free. The hyoidean arch is attached neither to the suspensorium, nor to the skull; its cornua are very slender, and no distinct body is developed; it is followed by several slender, hooplike, branchial arches. The mandible is dentigerous. Nothing is known of the early stages of development; but Müller discovered branchial clefts, with rudimentary branchial filaments, in young Coedlioe.

The Labyrinthodonta for the most part resembled the Urodela in the proportions of the tail and limbs to the body, but some (as Ophiderpeton) were serpentiform, and apparently apodal; no raniform Labyrinthodonts have yet been discovered. The vertebrae are amphicoelous. The mandible is dentigerous. The bones of the antebrachium and crus remain distinct, and the tarsus is not elongated. The manus and pes appear to have been pentadactyle. Three sculptured pectoral plates and a peculiar dermal armour of small scales, confined to the ventral face of the body, are present in many genera. Nothing is known of the early stages of development, but the γG ∖ mgArchegosauria appear to have possessed ossified branchial arches.

In giving a sketch of the organisation of the Amphibia, it will be necessary to enter much more fully into the characters of the skeleton than into those of the other systems of organs. ’

The Vertebral Column, Bibs, and Sternum.— Leaving the extinct Archegosauria aside for the present, all the Amphibia possess well-ossified vertebrae, the arches of which, in the adult condition (except, perhaps, in some Labyrinthodonts), are not separated by a neuro-central suture from the centra. The latter may be amphicoelous, as in the lower Urodela, the Peromela, and the Labyrinthodonta; or opisthocoelous, as in the higher Urodela and some Anura (e.g., Pipa and Bombinator) ; or procoelous, as in the majority of the Anura (with the exception of the eighth vertebra, which is usually amphicoelous; and of the ninth, which commonly has one convexity in front and two behind). In all the recent forms which have been examined, the centra and intervertebral masses contain more or less distinct remains of the notochord. The arches of the trunk vertebrae are connected by zygapophyses; the spinous processes are usually low, but attain a great relative length in the caudal region of some of the Labyrinthodonts (e.g. Urocordylus). Transverse processes are present in all the trunk vertebrae, except the atlas; they are shortest in the Peromela, longest in the Anura. In most Urodela, these transverse processes, at any rate in the anterior trunk vertebrae, are divided into two portions, a dorsal and a ventral, which diverge towards their free ends; or, more strictly speaking, these processes are made up of two subequal transverse processes, a dorsal “tubercular” process, and a ventral “capitular” process. Sometimes this division prevails throughout the whole length of the trunk, but, more commonly, the two transverse processes become fused into one, posteriorly.

In the long-bodied Urodela (Siren, Proteus, Amphiuma), only a small number of the vertebrae which succeed the atlas present traces of double transverse processes; further back, the coalesced transverse processes form trihedral projections, their dorsal and ventral contours converging instead of diverging, and giving a very characteristic aspect to these vertebrae.

In some Labyrinthodonts, the capitular and tubercular processes, divergent and subequal in some (probably the anterior) vertebrae, coalesce into one in other vertebrae; and the capitular division being shorter than the tubercular, transverse processes, like those of the middle thoracic region of the crocodiles, are thus produced.

In the Peromela, there is a short capitular process, but the tubercular process is represented by a mere facet placed below the prezygapophysis.

In the Anura, finally, the vertebrae have only a single transverse process (possibly representing the coalesced double transverse processes of the posterior trunk vertebrae of such Urodela as Menopoma), which, in some of the vertebrae, may attain a great length.

Bibs are present in a few Anura, in all Urodela, Peromela, and Labyrinthodonta; and, in the last-named and some Urodela, they attain as great relative dimensions as in other Vertebrata. But they are always vertebral ribs, no Amphibian being known to possess more than rudiments of sternal ribs. The atlas is never provided with ribs. In the Peromela, ribs are borne by all the other vertebrae, except the very hindmost. In the long-bodied Urodela, on the other hand, they are restricted to a few of the anterior vertebrae. In the other Urodela they are usually confined to the prse-sacral and sacral vertebrae; but, in some cases, one or two of the anterior caudal vertebrae have free ribs. The form of the proximal end of the rib corresponds with that of the transverse processes or process. Where this is double, the rib presents a fork, formed by the capitulum and tuberculum; and when the capitular and tubercular transverse processes are of equal length, the capitula and tubercula of the ribs are equal; but when either of the former is shorter than the other, the corresponding part of the rib is longer. The Peromela have no sternum, and that of the Labyrinthodonta (if they possessed any) is unknown. In the Urodela, the sternum never ossifies, and there is no trace of even a cartilaginous sternum in Proteus. In Menobranchus, there is a very small cartilaginous sternal plate, which sends lateral prolongations into two of the intermuscular ligaments, representing rudimentary sternal ribs.

In the Newts the sternum becomes a broad and stout plate of cartilage, with a median, posterior, cristate, xiphoid process, and with articular surfaces on its antero-lateral margins for the reception of the coracoids. The sternum attains its highest development in the raniform Anura, the xiphoid process becoming elongated and dilated at its extremity, and more or less converted into bone, while calcification of the body of the sternum itself may also occur.

In the Urodela, the first vertebra always presents two slightly concave articular facets, the faces of which look outwards and forwards to adapt themselves to the occipital condyles. Between these facets, the dorsal moiety of the anterior face of the centrum gives rise to a process, which is little more than a ridge in Proteus, but in other genera becomes very prominent, and has a curious resemblance to the odontoid process of the axis vertebra of a bird. This “intercondyloid” process of the atlas sometimes {Amphiuma, e.g.) exhibits on each side, near its termination, an articular facet, which plays on a corresponding facet of the adjacent face of the occipital condyle.

Mayer (Analecten, p. 10) was misled by the form of this process into the supposition that the vertebra to which it belongs is not the atlas, but the odontoid, vertebra. But there is a similar process of the first vertebra in the Rays, and the relations of the vertebra to the nerves show that it is certainly not the homologue of the axis vertebra of other Vertebrates. The first spinal nerve, which haa the distribution of the hypo-glossal of the higher Vertebrata, passes out of the spinal canal, either between the first and second vertebrae, or through a foramen in the arch of the first, in the Amphibia, which have no proper suboccipital nerve. This is a very curious circumstance, and requires elucidation by the study of development.

In the Anura, the atlas has the same general form, but the median process is either inconspicuous, as in Rana esculenta, or may be absent.

Among the Labyrinthodonta, the atlas of Mastodonsaurus only is known. It presents two concave facets anteriorly, separated for about half their length by a notch, which probably lodged a ligament.

The atlas of the Peromela has the two characteristic facets for the occipital condyles, but the intercondyloid process is absent, and the anterior margin of the arch of the vertebra projects forwards towards the corresponding margin of the occipital foramen (Epicrium).

In those Urodela which possess posterior limbs (except Proteus and Amphiuma), one vertebra, or sometimes two (Meno-pomai), are distinguished from the rest as “sacral” by having stouter ribs, the outer ends of which abut against, and are united by ligaments with, the ilia.

The Anura always possess a sacral vertebra (sometimes ankylosed with its predecessor or successor), the transverse processes of which are often enlarged, and sometimes greatly expanded, at their iliac ends. The characters of the sacrum of the Labyrinthodonta are not known.

In the Urodela, the anterior caudal vertebrae, except the first, have inferior arches, which, like the neural arches, are continuously ossified with the centra; and the same condition obtained in the caudal vertebrae of the Labyrinthodonts.

In the Anura, the caudal vertebrae are replaced by a long coccyx, consisting of an osseous style, to the dorsal aspect of the anterior end of which two neural arches are ankylosed. The anterior face of the style usually presents two concavities (one in Bombinator and some other genera), which articulate with the corresponding convexities on the posterior face of the centrum of the sacral vertebra. The number of the vertebrae in the spinal column of the Urodela and Peromela varies very much. In the long-bodied Urodela and Peromela they may be very numerous.

According to Cuvier, Caecilia has 230; Siren, 99; Amphi-uma, 75; in Menobranchus there are 18 prae-sacral and 25 caudal; in Salamandra, 15 and 26; and a similar variation appears to have obtained in the Labyrinthodonts. On the other hand, in the Anura the number of vertebrae (excluding the coccyx) is very constantly nine; though this number undergoes an apparent reduction, in some cases, by the ankylosis of the first and second vertebrae (Cera-tophrys dorsata, Pipa, Lactylethra, Breviceps), and in others by that of the sacral vertebra with the coccyx (Pipa, Dactylethra, Breviceps, Pelobates).

In the carboniferous Labyrinthodont, Archegosaurus, the notochord appears to have persisted throughout life, and the ossification of the centra of the vertebrae to have gone no further than the development of bony rings, such as those with which the ossification of the centra of the vertebrae of a tadpole commences.

The Cranium,.— The skull is always very depressed, and is usually broad in proportion to its length, though, in this respect, there is considerable variation, the skulls of Proteus, Menobranchus, and Amphiuma being narrow, when compared with those of Siredon, Menopoma, and the Anura. The occipital foramen is situated in the middle of the posterior face of the cranium, and there are always two occipital condyles. The long axis of the suspensorium, or pedicle by which the mandible is connected with the sidewalls of the brain-case, varies much in its direction— passing obliquely downwards and forwards in the lower Amphibia and in the larval condition of all, but swinging back until it stands out at right angles to the axis of the skull, or becomes directed downwards and backwards, in the higher Amphibia. The suspensorium is almost immovable upon the skull, being clamped thereto by the squamosal bone, besides being, as a general rule, united with some part of the wall of the skull by synchondrosis. The “primordial skull,” or chondro-cranium, usually remains, to a great extent, unossified, even in the adult. In the Urodela, the hyoidean arch· is always connected by strong ligaments with the suspensorium; but, in the Anura and in the Peromela, it becomes completely detached from the suspensorium, and may be free (Peromela), or acquire a new attachment to the periotic region of the skull in front of the fenestra ovalis (Anura).

The bones which are always present in the Amphibian skull are the exoccipital, pro-otic, parasphenoid, vomer, parietal, frontal, squamosal, premaxillary, palatine, quadrate, dentary, splenial, and angular. The basi-occipital and the basisphenoid are always absent, or are represented by mere partial calcifications of the chondro-cranium. There is always a fenestra ovalis closed by a stapes. The branchial arches do not exceed four pairs in number, and, in the perennibranchiate Amphibia, there are never fewer than three pairs.

The skull of the Frog (Figs. 4-7), as the most accessible member of the group, and that, the development of which has been most carefully studied, may be taken as the starting-point from whence to follow...