Foppa

FORAMINIFERA. This designation is part of that given by D’Orbigny in 1825 to an order of animals forming minute calcareous shells (found recent in shore-sand, and fossil in various Tertiary Limestones), for the most part many-chambered, and often bearing a strong resemblance in form (fig. 1) to those of Nautilus, Orthoceras, and other chambered Cephalopods,—his (supposed) Cephalopoda foraminifera being distinguished from the (real) Cephalopoda sipunculifera (Nautilus and its allies) by the want of the “siphon” which passes from chamber to chamber in the latter, and its replacement in the former by mere “foramina” in the dividing septa. And it seems to have been the applicability of this term Foraminifera to the shells thus characterized which has caused it to be retained as their ordinary designation, notwithstanding that the knowledge since acquired of the animals that form these shells necessitates the removal of the group from the elevated position assigned to it by D’Orbigny, to nearly the lowest grade of the whole animal series. It was by the admirable observations upon living Foraminifera published by Dujardin, in 1835, that attention was first drawn to the existence of a type of animals more simple than any previously known,—their bodies consisting entirely of an apparently homogeneous semi-fluid substance, to which he gave the name “sarcode”; and this substance projecting itself through apertures of the shell into indeterminate ramifying extensions (which he termed pseudopodia), capable of being retracted and fused again (so to speak) into the general mass of the body. Regarding these animals as a section of the large group of Infusoria, whose bodies he supposed to have a like simplicity of sarcodic composition, he distinguished them as Rhizopods, on account of the rootlike character of their pseudopodia! extensions.

The general correctness of Dujardin’s description of the animals that form Foraminiferal shells has been fully confirmed by subsequent researches; but the larger knowledge since obtained of the nature of the Protozoa has led to a more correct apprehension of the relations of the Rhizopoda to the other components of that group. What is now regarded as the simplest type of an animal, designated a Moner (see Animal Kingdom, vol. ii. p. 50), consists of an independent particle of the elementary form of living matter known as “protoplasm” (the “sarcode” of Dujardin), which is capable of growth and maintenance by the assimilation of nutrient material, and of multiplying itself either by subdivision or by some modification of that process. Now the first stage of differentiation of this apparently homogeneous substance into histogenetic elements consists in the appearance of certain rounded bodies termed endoplasts, which appear to be the equivalents of the nuclei of the “cells” whose individuation marks a higher stage of differentiation. And the next stage (well seen in Amoeba) consists in the differentiation of a more consistent external layer, or “ectosarc,” from the less consistent substance of the interior, or “endosarc,” in which are observable “vacuoles” containing fluid, of which one or more (that seem bounded by a definite pellicle, and are known as “contractile vesicles ”) contract and dilate rhythmically. As yet, however, there is no definite point of entrance for alimentary particles, or of exit for excrementitious matter,—nutrient τngesta being admitted, and their unassimilable residue being got rid of, through any spot of the ectosarc. It is in the presence of a definite mouth, and usually of an anus also, that even the simplest of the true ciliated Infusoria show a decided advance upon the “rhizopodal” type,—an advance which is still more marked in the higher Infusoria by the complexity of their internal organization.

Now the animal bodies of Foraminifera, notwithstanding the regularity and complexity of the shells they form, show but a very slight advance on the simplest moneral type. For their protoplasmic substance does not seem to be differentiated into “ectosarc” and “endosarc,”—every part of it alike projecting itself into pseudopodial extensions, and these extensions being capable, not only of dividing and ramifying indefinitely, but also of reuniting by mutual fusion when they come into contact with each other, so as to constitute an irregular network (figs. 2, 3, 4). It is on account of this last peculiarity that the writer has distinguished the reticulose forms of the Rhizopod type from the lobose (consisting of Amoeba and its allies) on the one hand, and from the radiolarτan (of which Actinophrys is the type) on the other. The sarcodic bodies of Foraminifera were believed until recently to have neither “nuclei” nor “contractile vesicles”; but as the observations of Hertwig and F. E. Schulze have established the presence of these in some instances (the writer also having observed “endoplasts” in Orbitolites), it is probable that they exist universally.

The attention which has been given in recent years to the study of Foraminifera, has invested the group—formerly considered as comparatively insignificant—with a new interest and importance. For (1) these minute testaceous Rhizopods, instead of having mere local habitats, are diffused abundantly through all save polar seas, and seem to do the first work of collecting by imbibition, and of converting into living substance, the organic matter which is contained, however sparingly, in all oceanic water, and the restoration of which, as fast as it is thus withdrawn, is effected by the various forms of marine vegetation. Again (2), without any thing that can be called organization, the protoplasmic bodies of these animals give origin to protective casings of marvellous regularity of form, and often of great complexity of structure,—these being sometimes “tests " built up by the apposition of sand-grains or other particles collected from the bottom on which they live, the animals only furnishing the cement by which they are held together, but being more often true “shells,” formed (like the skeletons of higher animals) by an interstitial deposit of carbonate of lime drawn from the surrounding medium, in the substance of living tissue. Notwithstanding (3) the absence of any perceptible differences in the character of the animals they respectively contain, these protective casings, whether sandy “tests” or calcareous “shells,” present a wide diversity of fundamental form, which is almost indefinitely augmented by subordinate modifications; and these modifications are generally so gradational as to render it impossible (when a sufficient number of specimens are compared) to draw any lines of separation between what appear, when only the extremes are regarded, to be clearly differentiated types. And this is true, not merely of species (which in the sense of constantly differentiated races cannot be said to have any existence among Foraminifera), but also of what would elsewhere be accounted genera·, whilst even families cannot, as a rule, be sharply defined, many of them containing aberrant forms that defy all attempts at strict limitation. In fact it would be scarcely a figure of speech to say that, within each of the three primary subdivisions of the group to be presently marked out, every form passes gradationally into every other. Hence the study of Foraminifera— whose small (but not too small) size and numerical abundance are peculiarly favourable to the comparison of large series of individuals—affords a most valuable lesson in taxonomy,—giving the best illustration that the whole animal kingdom can afford of the production of almost endless varieties of conformation by “descent with modification.” Looking (4) to the almost universal diffusion of existing Foraminifera, and to the continuous accumulation of their calcareous exuviae over vast areas of the ocean-bottom, there can be little doubt that they are at present doing more than any other tribe of marine animals to separate carbonate of lime from its solution in sea-water, so as to restore to the solid crust of the earth what is beiùg continually withdrawn from it by the solvent action exerted by rain and rivers upon the calcareous material of the upraised land. And when (5) we look back into the past history of our globe, we not only find conclusive proof of the enormous contributions which Foraminifera have made to the calcareous strata of Tertiary and Secondary epochs (Nummulitic Limestone and Chalk having been almost entirely formed by their agency), but encounter strong reason for the belief that the principal mass of the Palaeozoic Carboniferous Limestone had a similar origin. And when finally (6) we go still further back in geological time, and bring our knowledge of this type to bear on the very earliest calcareous formation that has yet been found in stratified rocks (the Serpentine Limestone of the Canadian Laurentians), we find distinct evidence that this also had its origin in Foraminiferal growth; which has thus stamped the impress of its existence even upon the oldest of those Archaic rocks, which, through a long subsequent succession, have as yet yielded no other distinct evidence of the existence of either animal or vegetable life on our planet. And thus in all parts of the geological series we not only recognize the constructive work of these humble organisms, but, interpreting the past by the present, find ever-increasing reason to believe that it has exceeded that of all other marine animals taken collectively.

A concise statement of the evidence in support of each of these positions will be embodied in the following sketch of the life-history, present and past, of this group; which will be so drawn as rather to bring into view its great features of general interest, than those details with which the systematist only is concerned.

Although the testaceous Foraminifera are all marine, certain shell-less animals essentially similar in nature occur in fresh water; and these, of which Liaeberkühnia (fig. 2) is a characteristic example, afford the best means of studying the life-history of the “reticulose” type. In its inactive state Lieberkühnia is an ovate corpuscle of granular protoplasm about l-400th of an inch in diameter, not presenting either any distinct differentiation of “endosarc’’ and “ectosarc” or “contractile vesicle,” or any ev ident “nucleus,” but including a large number of vacuoles filled with a homogeneous liquid. In its active state, on the other hand, the body puts forth a sort of stem, which soon branches irregularly in to pseudopodia; and these subdivide and ramify with great minuteness to an extent two or three times as great as that represented in the figure, the ramifications coalescing whenever they come into contact with each other, so as to form an irregular network which may be compared to an animated spider’s-web. This network serves to entangle either minute particles (such as chlorophyll granules) or larger bodies (such as Infusoria) that come in its way,—the former being transmitted to the central body by a sort of circulation (closely resembling the cyclosis of vegetable cells) which is constantly going on through the whole protoplasmic network, and the latter becoming enclosed in a kind of sheath formed by the blending of the neighbouring pseudopodia, which apply themselves to its surface and draw it into the central mass by their gradual contraction. Although destitute of any protective envelope, Lieberkühnia does not put forth its pseudopodia indifferently from any part of its surface,—their primary stem being enveloped in a transparent sheath, which may be traced as a thin pellicle over the whole body. And in Gromia (fig. 3), of which some forms inhabit fresh water (attaining a size that renders them visible to the naked eye), whilst others are marine, this pellicle is thickened into a distinct casing or “test” of ovoidal shape (probably composed of chitin), with a single round orifice of moderate size, through which the sarcodic body puts forth its pseudopodial extensions. When the animal is in a state of repose, these are entirely retracted into the test; but when its activity recommences, they are put forth from its orifice, as from the stem of Lieberkühnia, and form a sarcodic network which is in a state of incessant change—new centres of radiation often arising where two or more pseudopodia coalesce, by the flowing of the protoplasm towards those points. It is specially noticeable in this type that the sarcodic body extends itself over the entire surface of the test, so as completely to enclose it, and that pseudopodia are put forth from every part of this extension, being especially numerous at the posterior end, where they probably serve to fix the test, and thus to enable the animal to put forth more power in seizing the larger creatures that serve as its food. For whilst it is partly nourished by the minute granules that adhere to its outspread network, it lays hold of the smaller Infusoria and Diatoms, the zoospores of Confervae, &c., and draws them entire into the interior of the test, within which their indigestible remains may frequently be seen. Now, if the transparent pellicle of Lieberkühnia were consolidated by calcareous instead of by chitinous deposit, a monothalamous (single-chambered) “shell” would be produced (9 in fig. 1), such as constitutes the permanent form of the simplest Foraminifera, and the primordial form of even the most complex. This shell, like the test of Gromia, may have but a single aperture, from which the pseudopodial extensions are put forth, and through which alone nutriment is received into the contained body. But in a large proportion of the polythalamous (many-chambered) Foraminifera (fig. 4), the shell-wall is perforated with minute pores over its entire surface, through which pseudopodia extend themselves in a radial direction; and while the coalescence of these at their origin forms a continuous sarcodic layer that covers the exterior of the shell, the coalescence of their extremities forms new centres of radiation at a distance from it. The aperture or mouth in these types is much smaller than in the preceding, and appears to serve rather for the projection of the stolon-process, by which new chambers are formed (in the manner to be presently described), than for the introduction of nutriment. And when it is considered that the diameter of the pores of the shell never exceeds l-5000th of an inch (being often much less than 1-10,OOOth), and that the chlorophyll-granules, zoospores, &c., that nourish the fresh-water Rhizopods are altogether wanting in the sea-depths inhabited by the higher types of Foraminifera, there seems additional ground for the doctrine already propounded, that the nutrition of the animals of this group is mainly drawn rather from the organic matter that is dissolved in the medium they inhabit, than from solid particles suspended in it.

In regard to the propagation of Foraminifera, little is as yet certainly known. The growth of the individual may proceed, as will be presently shown, to an almost indefinite extent, by the gemmiparous multiplication of the segments or divisions of its body, with a corresponding multiplication of the chambers of its shell; but it more frequently happens that when the organism has attained a certain limited size, the new segments detach themselves, each one growing into the likeness of its parent; and this is probably the ordinary way in which the continuance of the race is provided for. But it would also seem that under certain circumstances the sarcodic body of the parent breaks itself up into segments, each containing an “endoplast” or “nucleus,” and that around each of these a shelly covering is formed while it is still enclosed within the original shell, the offspring finally escaping by its rupture. Whether this mode of propagation is preceded by any process of “conjugation,” and is thus related to sexual generation, is still undetermined.

By far the greater number of Foraminifera are composite fabrics, evolved from a simple protoplasmic body by a process of continuous gemmation, each bud remaining in connexion with the stock from which it was put forth; and according to the plan on which this gemmation takes place, will be the configuration of the composite fabric thereby produced. Thus if the bud be put forth from the aperture of the monothalamous Lagena (9 in fig. 1) in the direction of the axis of its body, if a second chamber be formed around this bud in continuity with the first (receiving the neck of the latter into its own cavity), and if this process be successionally repeated, it is obvious that a straight rod-like shell (10 in fig. 1) will be produced, having a series of chambers communicating with each other by the apertures that originally constituted their mouths, and opening externally by the mouth or aperture of the last formed chamber. The successive segments may be all of the same size, or nearly so; in which case the entire series may either resemble a string of beads, or may approach the cylindrical form, according to the shape of the chambers. But it more frequently happens that each segment somewhat exceeds its predecessor in size, so that the entire shell has a somewhat conical shape. If, on the other hand, the axis of growth should be slightly curved instead of straight, the resulting composite shell will be arcuate, while a more rapid deflection gives it a spiral curvature (5 and 11 in fig. 1). The form of the spire will depend in the first place upon whether its convolutions lie in the same plane, like those of a nautilus, so that the shell is equilateral (16 and 19 in fig. 1), or pass obliquely round a vertical axis, as in a snail, so that the shell becomes “inequilateral” (18 in fig. 1), having a more or less conical form, with the primordial chamber at its apex. In other cases, again, the vertical axis is greatly elongated, and the number of chambers forming each revolution around it is reduced to four, three, or even two (13 and 14 in fig. I). But further, the spiral plan of growth may give place to the cyclical, successive circles of new chambers being formed around the interior growth, so as to give the shell a discoidal shape (6 and 17 in fig. 1). And sometimes all regularity of plan disappears in the later stages of growth, new chambers being added in various directions, so that the fabric becomes “acervuline.”

In the older classifications of Foraminifera, these differences of plan of growth were adopted as characters of primary importance in the subdivision of the group. But it has now become obvious that comparatively little value is to be attached to them. For to associate together all rectilineal, all spiral, and all cyclical Foraminifera, is not only to run counter to the indications of natural affinity that are furnished by the intimate structure of the shell, the conformation of the individual chambers, and the mode of their intercommunication, but to set at nought two general facts of fundamental significance,— first, that one plan of growth often graduates insensibly into another, as does the straight into the spiral in the group of which 10 and 11 of fig. 1 are extreme forms; and, second, that it is not at all uncommon for the plan to change during the growth of one and the same individual,—the spire, for example, either straightening itself out, so as to revert to the rectilinear type, or returning into itself so as to make a complete circle, round which a succession of concentric annuli is then produced on the cyclical type, while the original regularity is sometimes lost altogether in the “acervuline” piling up of the later-formed chambers. On the other hand, the fundamental importance of the perforation or imperforateness of the external envelope, as affecting the physiological condition of the contained animal, is now universally admitted. For where (as in Peneroplis, 5 in fig. 1) that envelope, whether composed of calcareous shell or built up by the cementation of sand-grains, has no other communication with the exterior than by the single or multiple aperture of the last chamber through which the whole pseudopodial apparatus of the contained animal is put forth, the nutrition of the entire segmental body that occupies the previously formed chambers must be carried on by a continual interchange of protoplasmic substance extending through the entire mass, however great may be the multiplication of its segments. Where, on the other hand (as in Rotalia, fig. 4), the wall of each chamber is perforated for the passage of pseudopodia, the segment it contains is thereby placed in direct communication with the surrounding medium from which it derives its sustenance, so as to be independent of the remainder of the series. The “imperforate” calcareous shells of Foraminifera are also termed “porcellanous,” from the opaque-white aspect they present when viewed by reflected light; though, when thin, they show a rich brown hue by transmitted light. Even under ⅜ high magnifying power, their substance appears entirely homogeneous. The perforated shells, on the other hand, having an almost glassy transparence (except where this is interrupted by tubulation), are known as “vitreous” or “hyaline.” Where the shells are thin, the perforations are simply pores (fig. 4); but where they are thick, the perforations are tubules usually running straight and parallel from surface to surface (fig. 24¾ Thus, then, the Foraminifera are naturally divisible in the first instance into two groups, the Imperforata and the Perforata; the former of which is again divisible into the Arenacea, which build up “tests” by the aggregation of sand-grains, and the Porcellanea, which form porcellanous shells; whilst the latter, Vitrea, includes all the perforate types. There is often a very curious parallelism between the forms contained in these three series respectively, still more between certain “porcellanous” and certain “vitreous” types; but this arises in each case from similarity in plan of growth, and does not indicate any real affinity. In fact the two calcareous-shelled series may be compared to two trees of different orders, which resemble each other in their mode of branching, but have dissimilar leaves and flowers.

I. Arenacea. —The calcareous shells of certain types of Foraminifera, alike in the “porcellanous” and in the “vitreous” series, are not unfrequently covered with sandgrains, cemented into the surface-layer of the true shellsubstance. But in the group now to be described, the casing of the body is entirely composed of foreign particles (usually grains of sand, but sometimes minute Foramintfera, sponge-spicules, &c.), the animal furnishing nothing save the cement that holds them together; and in its lowest forms no special cement seems to be supplied, the sandgrains being simply imbedded in the sarcodic substance of the body. The increased attention which has of late been given to this group (our knowledge of which has been largely augmented by deep-sea dredging) seems to justify our regarding the “arenaceous” type as on the whole less advanced thaneitherthe “porcellanous” or the “vitreous,”— its lowest forms presenting a condition less specialized than even the simplest of the calcareous-shelled Foraminifera, whilst its highest, although sometimes attaining a comparatively gigantic size, build up their massive “tests” upon a very simple plan, exhibiting no approach to the complexity of structure tobe found in the “shells” which some of them closely resemble in external form. A few of the more interesting types of the Arenaceous group will now be briefly noticed.

In the sandy mud which covers certain parts of the bottom of the 500-fathoms channel between the north of Scotland and the Faroes, the large monothalamous Astrorhizae are sp abundant as sometimes to form a great part of the contents of the dredge. Their typical shape (as the name implies) is discoidal with stellate radiations; but they are sometimes globular, sometimes cervicorn, and present every intermediate gradation between these forms. The “test” is composed of loosely aggregated sand-grains, not held together by any mineral cement; and it is destitute of any definite orifice, so that the sarcode-bqdy (of a dark green colour) which occupies the cavity must put forth its pseudopodial extensions between the sand-grains of its test. But there is, in the writer’s belief, a lower form even than this. For in the same dredgings there were found a number of little globular masses varying in size from a pin’s head to a large pea, formed of aggregations of sand grains, foraminiferal shells, &c., held together by a tenacious protoplasmic substance, without any definite structural arrangement. And although these might be supposed to be mere accidental agglomerations, yet there seems adequate reason for regarding them as living organisms of the simplest possible “monerozoic” type. For just as a simple “moner,” by a differentiation of its homogeneous protoplasm, becomes an Amaeba, so would one of these undifferentiated mixtures of sand and protoplasm, by the separation of its two components—the sand being limited to the superficial layer, so as to form an investing “test,” of which the whole interior is occupied by the sarcode-body alone,—become an Astrorhiza.

The next degree of elevation is shown in the presence of a distinct aperture or mouth, the sand-grains surrounding which are generally held together firmly by a ferruginous cement, even when those of the remainder of the test are as loosely aggregated as in Astrorhiza. One of the most common forms of this type is a simple cylindrical tube, closed at one end, but having a conical neck with a circular orifice at the other. And in a still higher type, this cylinder is divided into a succession of chambers, each of which opens into the next by a conical orifice bordered by cemented sand-grains, while the last opens externally by a like orifice,—thus sketching out the nodosanne” type of the “vitreous” Foraminifera, but on a much larger scale.

In the more advanced Arenaceous types, on the other hand, the sand-grains of the entire “test” are firmly united together by a cement composed of phosphate of iron, which must be exuded from the sarcodic body of the animal, its materials being originally derived from the sea water. In some instances the sand-grains selected are of such minute size that, when worked up with the cement, they form a sort of “plaster,” the surface of which is quite smooth, both externally and internally. This is the case with the genus Trochammina, under which is ranged a. whole series of forms ranging from a simple undivided tube to a perfect helical spire resembling a Catherine-wheel (whence the name given to the genus), and thence, by the alteration of its spire to the turbinoid, and by the subdivision of its cavity into chambers, to the “rotaline” type. In other instances the sand-grains are somewhat larger, but are apposed with such extraordinary regularity, and cemented together so artificially, as to form a most delicate but firm test of very uniform thickness, perfectly smooth both externally and internally. Tests of this kind present a singular series of adumbrations of the “orbuline,” “globigerine," and “nodosarine” types of the vitreous series. In other cases, again, the sand-grains being larger, the “test” is constructed more coarsely, but still with remarkable symmetry. One of the most interesting of the simple coarse-grained forms is the little Saccammina spherica, whose flask-shaped tests (fig. 5, a, b} of the size of minute seeds, with prolonged necks and circular apertures, now found living abundantly in particular localities, have been also distinctly recognized in Carboniferous Limestone. That the size of the sand-grains used in the construction of such tests is not accidental (depending on the fineness of division of the sandy bottom on which the animals live), but is the result of selection on the part of the animals that use them, is shown not only by the fact that coarsegrained and fine-grained “tests” are brought up from the same bottom, but by the very curious difference in the materials used to form two kinds of tests nearly of the same size and of corresponding simplicity of type. The very same deep dredgings which yielded Saccammina brought up a number of other monothalamous spherical tests, filled with dark green sarcode, to which the name Pilulina has been given from their resemblance to homoeopathic globules (fig. 5, d). These, instead of being constructed by the cementation of sand-grains, are composed of a sort of felt (β) made by the regular “laying” of siliceous fibres (thefine-pointed ends of elongated sponge spicules) with very minute sand-grains dispersed among them; and the aperture, instead of being a round hole at the end of a short neck, is a sigmoid fissure with somewhat projecting lips. The constancy of these differences indicates a dissimilarity in the “potentialities” of the animals of the respective types, of which we find no indication in their apparently-homogeneous sarcodic bodies.

The highest development of this type known to exist „at the present time is shown in the large polythalamous “nautiloid” forms which have been brought up in considerable abundance from depths mostly ranging between 200 and 500 fathoms. The test (fig. 6, a) is for the most part composed of coarse sand-grains firmly cemented to each other; but it is generally smoothed over externally with a kind of “plaster” resembling that of which the “trochammiιie” tests are made up. On laying open the spire, it is found to be very regularly divided into chambers by partitions formed of cemented sand-grains (δ), a communication between these chambers being maintained by a fissure left at the inner margin of the spire. So far, the plan of structure accords with that of the smaller, “nonionine” forms (resembling 19 of fig. 1), which aie found at much greater depths, ranging downward to more than three miles. But this more developed form is characterized by the extension of the principal cavity of each chamber into passages excavated in its thick external wall,—each passage being surrounded by a very regular arrangement of sand-grains, as seen at c. This “labyrinthic” structure is of great interest, from its relation on the one hand to the still higher development of the like structure in the large fossil Lituola of the Chalk, whose crozier-like “test” has its principal chambers subdivided into “chamberlets,” and on the other hand to that of two gigantic fossil Arenacea, one of the Cretaceous and the other of early Tertiary age.

Geologists who have worked over the Greensand of Cambridgeshire have long been familiar with solid spherical bodies, varying in size from that of a pistol-bullet to that of a small cricket-ball, which there present themselves not unfrequently, and have been regarded by some as mere mineral concretions, whilst others supposed them to be fossilized Sponges. They prove, however, to be “tests” of Arenaceous Foraminifera, which are distinguished from all other known foraminiferal types by their concentrically-spherical plan of growth (fig. 7),—the successive spheres being formed around a

“nucleus,” which consists of a succession of chambers arranged sometimes in a straight line and sometimes in a spiral, the last of them opening out and extending itself over its predecessors. Each sphere contains a set of principal chambers, with labyrinthic extensions of them, corresponding in all essential particulars with those of the nautiloid Lituola just described; so that there is nothing except its large size (which simply results from continuity of increase and spherically-concentric plan of growth) to differentiate Parkeria from ordinary Foraminifera. It is not a little interesting to find the very same plan of construction earned out under a different form in another gigantic fossil Arenacean, probably of the early Tertiary period, termed Loftusia; which, agreeing with Parkeria in all essential particulars, differs from it in plan of growth, Loftusia being formed, like Alveolina (fig. 10), by the rolling of a spiral round an elongated axis.

The discovery of these two singular types greatly enlarges our conceptions of the Arenaceous group, and shows how little justification there is for any attempt to lay down a priori restrictions as to the supposed “possibilities” of Foraminiferal organization. ,

II. Porcellanea. —In the sketch now to be given of the “porcellanous” series, it will be the writer’s object to show the closeness of the relation between its simplest and its most complex and diversified forms (which he regards as all constituting but a single family, the Miliolidd), and to indicate the chief of those gradational transitions by which a continuous affinity is established between them all.

Passing by the proteiform Nubecularia,— the tent-like incrusting shells of which rudely foreshadow almost every plan of growth to be met with among higher Foraminifera,—we commence with the simple Cornuspira (1 in fig. 1), whose spirally-coiled undivided tube, the exact isomorph of the helical arenaceous Trochammina, attaches itself to the Zoophytes and Sea-weeds of the British coasts. In full-grown specimens, the later turns of the spire generally flatten themselves out, like those of Peneroplis (5 in fig. 1), so that the form of the mouth is changed from a circle to a long narrow slit. From this simple undivided spire we may pass along two divergent lines, one conducting us to the milioline and the other to the orbiculine type, and the latter again leading us to the orbitoline, in which the spiral plan of growth gives place in the very earliest stage to the cyclical. The shells of the Miliolae (so named from their resemblance to millet-seeds) are at present found in the shore sands of almost every sea; and they accumulated in certain localities during the early Tertiary period to such an extent as to form massive beds of limestone. Their typical forms (3 and 4 in fig. 1 ) are composed of a succession of elongated chambers, usually arranged bi-serially on the opposite sides of a straight axis (3 in fig. 1), at one of the ends of which each chamber opens forwards into that which follows, whilst at the opposite end it opens backwards into that which preceded, the aperture in either case being partially closed by a “tongue” or “valve” (which may be considered an imperfect septum), as shown at 4, fig. 1. Indications of such a division may be sometimes noticed even in Cornuspira, but it shows itself fully in Spiroloculina, in which the spire has the form of an ellipse, at the two ends of whose major axis the new chambers commence alternately. The spiral plan of growth here remains obvious throughout; but in the typical Miliolines (3 and 4 in fig. 1) it is more or less obscured by the extension of the later chambers over the earlier, giving rise to the varied forms which have been distinguished under the generic names of Biloculina, Triloculina, and Quinqueloculina, according to the number of chambers visible externally. The extreme inconstancy, however, which is found to mark this distinction, when large numbers of specimens are compared, entirely destroys its value as a differential character. Milioline shells, though frequently quite smooth, often show some kind of “sculpture,” their surface being sometimes more or less deeply “pitted,” sometimes regularly honeycombed, and sometimes longitudinally ribbed; and these diversities have been largely used for the characterization of species. Here again, however, the examination of a sufficiently large collection shows the futility of any such differentiation, since every gradation is found between the smooth and the most sculptured forms, while it is not at all uncommon for one and the same shell to be smooth on some parts of its surface, and deeply pitted, honey-combed, or ribbed on others— making it obvious that such differences have no more than a varietal significance. There is not, in fact, any group in the whole Animal Kingdom of which the study is more instructive than that of the Miliolines, in regard to the extent of variation which is compatible with conformity to a fundamental type.

The culminating form of the Milioline type may be considered to show itself in Fabularia, a fossil of the Paris Tertiaries not known to exist at present, in which the principal chambers are subdivided into “chamberlets,” as ití,Orbiculina and Orbitolitcs, and the aperture is cribriform instead of single, the chamberlets opening externally by separate pores.

The undivided helical tube of Cornuspira, again, graduates through Hauerina and the spiral forms of Vcrtcbralina into the typical Pcne∙ roplis (fig. 8), a beautiful little shell that abounds in the shallow watersof many parts of the Mediterranean, and is remarkable alike for its glistening porcellanous surface, for the constancy of the ridge and furrow sculpturing winch crosses the intervals between the septa, and for the flattening-out of its spire, and consequent narrowing and elongation of its septal plane (5α in fig. 1), which is perforated by a single linear series of pores. In tropical seas, however, this type shows itself under a very different aspect (fig. 9). The spire, instead of being flattened out, is turgid; and the septal plane, instead of being perforated by a linear series of pores, has a single large aperture, the dendritic shape of which has caused the name Dcndritina to be assigned to this type. Now, although such marked differences between Molluscan shells would undoubtedly iustify generic differentiation, yet among Foraminifera they prove to bo not even of specific value; for when a sufficiently extensive series of this type is compared, its extreme forms graduate insensibly one into the other. In proportion apparently to the warmth of its habitat (the gradation being well seen in the Red Sea examples) the shell becomes less flattened and the septal plane broader, and the single row of pores becomes a double or even a triple scries, the pores of different scries being sometimes partially confluent. With a further increase in the turgidity of the spire, and with a progressive widening of the septal plane at the expense of its length, the pores lose their linear arrangement, and run together in groups, so as to form several irregularly fissured openings; and it is by the coalescence of these that the single dendritic aperture is formed in those examples whose general shape most nearly approaches that of Nautilus. This transition often shows itself in the successive stages of growth of one and the same shell. When we consider the physiological import of this variation, we find that it has no relation to any essential differences in the conformation of the animal,— all that it means being that the sarcodic pseudopodia, which issue separately in the one case, issue collectively in the other. It is interesting to remark, further, that in each of these types the spire often straightens itself out, so as to give to the shell the shape of a crozier (these “spiroline” forms being peculiarly common in the Red Sea), and that throughout the entire series the surfacemarking is singularly constant.

From this simply-chambered type we pass on to that in which each chamber is more or less completely divided by transverse partitions (or secondary septa) into a series of “chamberlets,” giving to the shell what is designated the “labyrinthic” structure. The first stage of this division, shown in figs. 11, 12, consists in a succession of contractions by which the sarcodic segment that occupies the cavity of each chamber acquires a moniliform or bead-like shape,—the sub-segments into which it is partially subdivided being connected by a continuous band or “stolon.” And even where the separation of the chamberlets is most complete, there is still an aperture in each secondary septum, by which the lateral continuity of the sub-segments is maintained. The relation of the labyrinthic Orbiculina (6 and 8 in fig. 1), common in tropical seas, to the simple “pencropline” type, is well seen in the early stage (7 in fig. 1) of the former, which is obviously a Pcncroplis with subdivided chambers. But as age advances, a remarkable change takes place. The later turns of the spire very commonly grow completely over the earlier, so as to make the umbilicus protuberant, as shown at 8 in fig. 1; and their thickness progressively increases by the vertical elongation of the sarcodic “blocks” that occupy their chamberlets into “columns,” which communicate with the exterior and with each other through several ranges of marginal pores. In the very large and hict l ly developed forms of this type (attaining a diameter of 7 or 8 lines), which make up the Tertiary Limestone of the Malabar coast, each surface of the spire has a thin layer of chamberlets divided off from the intermediate columnar portion, as in the “complex” type of Orbitolitcs to be presently described.

Now if the axis round which this Orbiculine spire revolves were to undergo such an elongation (by a multiplication of its subsegments in that direction) as to equal the diameter of the spire, the form would be changed to the globose, with a crescentic septal plane perforated by numerous separate pores; and a yet further increase in the comparative length of the axis would evolve the “fusiform” type characteristic of Alveolina (fig. 10), with an elongated and straightened septal plane showing several ranges of sepa rate pores. The largest specimens of this type at present known seldom exceed 0 ’ 4 inch in length; and are greatly surpassed by those massive forms of the early Tertiaries whose accumulation in Earticular localities produced what is now known as the Alvéolite imestone.

Sometimes, on the other hand, even at an early age, the growing margin of Orbiculina extends itself laterally at both extremities, so that the two extensions meet on the opposite side of the original spire, which is thus completely enclosed by it. Its growth is thence forth cyclical instead of spiral, concentric rings (each of them answering to one of the chambers of Peneroplis) being successively added, as shown at 6 in fig. 1, and the chamberlets into which they are subdivided opening by separate pores, usually arranged in several series, around the whole margin of the disk. Now, this is the plan of growth characteristic of Orbitolites, a type first known as fossil (abounding in the Calcaire grossier and other calcareous Eocene strata), but of which living forms have been since found abundantly in tropical and sub-tropical seas, frequently attaining a diameter of 8-10ths of an inch, and a thickness approaching l-6th. While marginal portions of the disks of the cyclical Orbiculina could not be distinguished from those of certain forms of Orbitolitcs, there is such a difference in their origins and early histories as necessitates their generic separation. For in the typical Orbitolite the plan of growth is cyclical from the first, successive rings being formed around a “nucleus,” which is never overlaid by later growths; and this nucleus consists of a “central” segment (a, figs. 11 and 12), which is more or less completely surrounded by a “circumambient segment” (δ), that gives off numerous radiating stolon-processes to form the first ring of sub-segments. It is a fact of no small morphological interest, however, to find among the varietal forms of this type a distinct reversion to the spiral origin,—the most complete example of it being presented in the deep-sea 0. tenuissimus, whose “nucleus” resembles a Comuspira of three or four turns, of which the last turn rapidly opens itself out, showing a primary division into chambers and a secondary into chamberlets, thus distinctly connecting with the ordinary Milioline type the form whose plan of growth appears at first sight most fundamentally different. This plan is most readily apprehended by examining such small “simple” forms of this type (figs. 11, 12) as occur in the Aegean and Red Seas, in which the successive rings continue to be formed on the pattern of the first. Each chamberlet of the shell (fig. 11) is connected by a passage with those on either side of it; and it is from these intermediate passages, not from the chamberlets themselves, that the radiating passages proceed which lead to the chamberlets of the next ring, or which, in the case of the outermost ring, open at the margin between the protuberant walls of the chamberlets. So, in looking at the sarcodic body (fig. 12) of the animal which occupied the ⅛ell, we see that it consists of a succession of necklace-like rings, each consisting of an annular cord with bead-like enlargements at regular intervals, and giving off from the intervals between these beads the radiating stolon-processes which give origin to the sub-segments of the next annulus, as shown at the margin cf the figure. These, extending themselves laterally at the growing edge of the shelly disk, will coalesce into a continuous cord, and a new ring of shell-structure will be formed by an excretion of calcareous matter from its surface. There is here no differentiation of parts whatever, every ring beiug a precise repetition (except as to number of parts) of that which preceded it; and in the living condition the semi-fluidity of the sarcode-body will allow of a perfectly free communication being kept up throughout the disk, so that nutrient matter taken in at the margin may be readily conveyed towards the centre. The uniformity in the endowments of the segments is shown by the fact, of which accident has repeatedly furnished proof, that a small portion of a disk entirely separated from the remainder, will not only continue to live, but will so increase as to form a new disk (fig. 13) whose concentric annuli form themselves regularly around the fragment, obviously by the extension of the annular sarcodie band from its proper growing margin around its whole periphery,— a fact of extreme significance, as showing that even in this elaborately constructed shell the animal body retains its original protoplasmic homogeneousness.

A yet greater complexity of structure presents itself in the large Orbitolite-disks of tropical seas, as also in those of whose fossil remains many Tertiary Limestones are chiefly composed. This complexity depends, in the first place, on the vertical elongation of the sub-segments into a columnar form, so as to produce a progressive thickening of the disk from the centre towards the margin, by which it comes to acquire a somewhat biconcave form; and with this there is an increase in the number of radiating stolon-processes, showing itself in a vertical multiplication of the ranges of marginal pores. The ends of the columns of each ring are connected laterally by two annular cords; and from each of these is given off a series of subsegments, that forms a layer of chamberlets on either surface of the disk, having no communication with those of the intermediate columnar structure except through the annular passages. Even this morphological differentiation does not seem connected with any diversity of function; and a careful comparison of a sufficiently extensive series of forms, from the most simple to the most complex, renders it clear that they are gradationally connected, the transition being a process of “evolution,” on which heat (probably coupled with a more copious supply of food) exerts an important influence.

III. Vitre a. —The vitreous-shelled Foraminifera constitute the most elevated division of the group, in regard alike to the high organization of their shell-substance, and to the elaborate construction shown in the shells of its most developed types. And it is in this division that we find the multiplication of individuals accomplishing by far the greater part of those two vast operations now in progress (as they seem to have been through all Geological time of which we know anything), which have been already specified as the great functions of the group:—the extraction from sea-water (1) of the minute quantity of organic matter universally diffused through it, which is converted into a protoplasmic substance fit to serve as food for higher animals, and (2) of the minute quantity of carbonate of lime held by it in solution, which is solidified into the substance of the shells whose accumulation gives rise to calcareous deposits on the ocean-bottom. The Vitreous Foraminifera may be grouped into three families, Lagenida, Globigerinida, and Nummulinida, the typical forms of which are distinguished by well-marked characters.

The chief feature of interest in the Family Lagemida is the unbroken succession of forms it presents, from the simple monothalamous Lagena to the complex polythalamous Cristellaria,— all characterized by the very minute tubulation of the shell-substance, and by the circular form of the aperture of each chamber, which has usually an everted lip marked by radiating furrows. The Lagena (9 in fig. 1) is a minute flask-shaped shell, with a prolonged neck, having the mouth at its extremity; and its external surface usually presents some form of sculpture, such as prolonged ribs, separate tubercles, or honeycomb areolation. In Nodosaria (10 in fig. 1) we find a rectilinear succession of similar chambers, the neck of each received into the cavity of the next; while in Cristellaria (11 in fig. 1) a series of progressively enlarging chambers, still presenting the characteristic radiate aperture, is arranged in a nautiloid spiral. These composite types, which are connected by a series of intermediate degrees of curvature, show also the characteristic sculpturing of the simple Lagena with an endless variety of modifications; so that there is no group of Fbraminifera which presents a more complete gradation between extremes so extremely diverse in form and surface-marking that, taken alone, they might fairly be adopted as types of distinct genera. Thus, as Mr H. B. Brady justly remarks, “if the word ‘species’ is anything more than a conventional term, the whole ought to constitute a single species. But governed by the exigencies of a partially artificial arrangement, the modifications embraced in this single unbroken series constitute thirteen genera, or almost two entire families, in Professor Reuss’s classification; while how many hundreds, if not thousands, of so-called ‘ species ’ have been founded upon the trivial characters above enumerated, it would need much patience to ascertain.”

This variability shows itself also in the curious “polymorphism” sometimes exhibited during the growth of one and the same individual, which is especially characteristic of the genus Polymorphlna. The young shell of this type is obviously made up of lageniform chambers regularly arranged in a double series alternating on the two sides of a rectilinear axis (13 in fig. 1); but from this plan there are often very wide departures in later stages of growth, both in the form and in the arrangement of the chambers,—one of the most curious consisting in the backward prolongation of the last chamber over all that preceded it, and its extension into “stags-horn processes,” which completely disguise the original conformation. In this aberrant type the characteristic “sculpturing” of the typical Lagenida is generally wanting,—the shell in its young state being peculiarly thin and glassy; whilst in the large “wild-growing ° forms the wall of the outer chamber is usually smooth, and has a porcellanous opacity.

The fundamental characters of the Family Globigerinida, which essentially consist in the coarse porosity of the shell (the pores being often τι ⅛- σ th of an inch in diameter), and in the fissured, crescentic, or semioval form of the aperture of each chamber, are well seen in the typical genus Globigerina, the principal agent in that production of globigerina-ooze which is now repeating (rather, perhaps, continuing) the formation of the old Chalk. As obtained from the bottom by sounding or dredging, the Globigerina presents itself in the form shownin fig. 14,—that is, as an aggregation of nearly spherical chambers, having coarsely porous walls like those of Rotalia

(fig. 4), and cohering externally into a more or less regular turbinoid spire, each turn of which consists of four chambers, progressively increasing in size. These chambers, whose number seldom exceeds sixteen, do not communicate directly with each other, but each has its own separate mouth, opening into a common “vestibule” which occupies the centre of the under-side of the spire. The younger shells, consisting of from eight to twelve chambers, are thin and smooth; but the older shells are thicker, and are raised into ridges that form a hexagonal areolation round the pores (fig. 15, α); and this thickening is shown, by examination of thin sections of the shell (b) to be produced by an exogenous deposit (corresponding with the ‘ ‘ intermediate skeleton” of the more complex types) that invests the original shell-wall, sometimes containing little flask-shaped cavities filled with sarcode (Wallich). When taken alive by the tow-net, however, floating at or near the surface, the shells of Globigerinoc are found to be beset with multitudes of delicate calcareous spines, which extend themselves: radially from the angles at which the ridges meet, to a length equal to four or five times the diameter of the shell (fig. 16).

‘ ‘ When the living Globigerina is examined under favourable circumstances, the sarcodic contents of the chambers may be seen to exude gradually through the pores of the shell, and spread out until it forms a kind of flocculent fringe round the shell, filling up the spaces among the roots of the spines, and rising a little way along their length. This external coating of sarcode is rendered very visible by the oil-globules, which are oval, and filled with intensely coloured secondary globules, and are drawn along by the sarcode, and may be seen with a little care following its spreading or contracting movements. At the same time an infinitely delicate sheath of sarcode, containing minute transparent granules, but no oilglobules, rises on each of the spines to its extremity, and may be seen creeping up one side of the spine and down the other, with the peculiar flowing movement with which we are familiar in the pseudopodia of Gromia. If the cell in which the Globigerina is floating receive a sudden shock, or if a drop of some irritating fluid be added to the water, the whole mass of sarcode retreats into the shell with great rapidity, drawing the oil-globules along with it; and the outline of the surface of the shell and of the hair-like spines is left as sharp as before the exodus of the sarcode.”

When a sample of the surface-layer of the “globigerina-ooze” is brought up from the sea-bottom by the sounding apparatus or the dredge, the shells are found for the most part perfect, except in the want of spines, but are of a more opaque whiteness than those captured near the surface, and hence have been supposed to be dead. This difference of aspect, however, may be attributed to the increase in the thickness of the shell by exogenous deposit, which is doubtless the cause of the like change in Polymorphina∙, and as a large proportion of these bottom-shells have their chambers filled with sarcode exactly resembling that of the types which unquestionably live at the bottom, the fact that in their young state they are found floating in the upper waters does not appear to the writer a sufficient disproof of the previously accepted belief that they live also at the bottom. And the fact that the thickened shells, when filled with their sarcodic contents, are so much heavier than sea-water as at once to sink to the bottom when placed in a vessel of that liquid seems strongly to indicate that so soon as adult growth (with successional increase in the number of chambers) has been attained, the carbonate of lime which the animal continues to separate from the sea-water is applied to the thickening of the shell, which will then sink to the bottom of the sea in virtue of its increased specific gravity. And since other Foraminifera undoubtedly pass their whole lives on the ocean-bottom, drawing their sustenance from sea-water in the manner already explained, there seems no reason why the subsidence of Globigerinae to similar depths should put an end to their vital activity. It is only in the surface-stratum of the globigerina-ooze, however, that the shell-chambers are occupied by sarcodic bodies. Its sub-surface layer consists partly of still recognizable fragments of the shells, diffused through a mass of amorphous particles, which appears to be the product of a still further disintegration of their substance; whilst the yet deeper layers of the “ooze” consist entirely of amorphous particles, all trace of shells being lost. It was observed in various parts of the “Challenger” voyage that in particular areas the “globigerina-ooze” was altogether wanting (being replaced by a red clay, probably resulting from the metamorphosis of volcanic products), even though the living animals were found as usual in the upper waters; and the absence of this calcareous deposit on the sea-bottom seemed attributable to the pressure resulting from its very great depth,—between 2500 and 3000 fathoms,—which, with the aid of carbonic acid contained in all sea-water, λvould exert a solvent action, thus restoring to it these portions of the great calcareous deposit of which the materials had been drawn from it by the living Globigerinae.

The higher forms of the Globigerine type constitute two principal series, in one of which the chambers succeed each other along a straight axis, whilst in the other they form a spire. One of the most common types of the first group is the Tertularia (14 in fig. 1), in which the chambers are arranged bi-serially, those of the two sides alternating with each other, and each communicating with the chamber above and below it on the opposite side; as is well seen in the “internal cast” (fig. 17, A), which is an exact model

(in glauconite or some other ferruginous silicate) of the sarcodic body that occupied the shell. The type of the second group is the almost universally diffused Rotalia, in which the chambers are disposed in a turbinoid spire (18 in fig. 1), through which passes a continuous stolon-process (as shown in the internal cast, fig. 17, B), lying on the lower and inner side. Of this type there are several very interesting modifications. Thus, in Discorbina (15, fig. 1) the chambers are flattened out over the surface to which the shell adheres; while in Planorbulina (17 in fig. 1) the early spiral plan soon gives place to the cyclical, and the shell thenceforth spreads, by concentric additions, over the surface to which it adheres. In those most-developed forms of this type which occur in warmer seas, the later-formed chambers do not merely surround the earlier, but are piled up more or less regularly upon them; and we find such aggregations spreading over the surfaces of shells, or clustering round the stems of zoophytes. Two of the most remarkable modifications of the planorbuline type, which strikingly illustrate the extremely wide range of variation among Foraminifera, are Polytrema and Orbitolina. The former, which was described by Lamarck as a coral, under the name of Millepora rubra, is a very common parasite upon shells and corals from the warmer seas,—sometimes spreading itself out horizontally in the form of a depressed cone, sometimes rising up from a small base in an arborescent growth, and sometimes developing itself into knobby excrescences. In all these varieties, the structure of the individual chambers, and their mode of communication with each other, remain essentially the same,— the diversity in the aggregate forms being simply due to the want of any definite plan of increase. The Orbitolinae (Lamarck), which occur abundantly in certain beds of Chalk, seem to have been gigantic forms of the planorbuliue type, represented at the present time by some comparatively minute organisms found on the Australian coast, which commence life as Planorbidinae, and then, by the sequential addition of chambers both above and below, as well as at the margin, come to acquire a sugar-loaf or a globular form. The size of the globular examples of fossil Orbitolinae, which, like the flints of chalk, are often found in Tertiary strata., varies from that of a small pea to that of a large bullet. There is a spreading Orbitolina in the Chalk, which sometimes attains the extraordinary diameter of four inches. These forms are of peculiar interest, as showing the tendency of the Foraminifcral type to that indefinite Zoophytic extension, of which we have the highest example in the ,Éozoön to be presently described.

The highest forms of the Rotaline type (which are confined to tropical seas) correspond with those of the “Nummuline” in the complexity of the organization of their shells, which only reveals itself to microscopic investigation. Each chamber has its own complete chamber-wall, so that the partitions which separate two contiguous chambers are double; and between these we find an additional deposit of calcareous substance, which the λvriter has designated as the “intermediate skeleton.” This deposit is channelled - through by a set of canals distributed upon a regular plan, and altogether forming a * ‘ canal-system” (fig. 18). These do not communicate directly with the chambers, but give passage to sarcodic extensions formed by the coalescence of pseudopodia that have passed through the pores of the proper chamber-walls. And as the development of this “canal-system’’ is exactly proportionate to that of the “intermediate skeleton,” it may be affirmed with some confidence that, as the formation of the latter proceeds, in the first instance, from the sarcodic expansion which covers the exterior of the chamber-walls, so it is continued by the prolongation of that expansion into the “canal-system.” Now, in Calcarina (so named from its resemblance to a spur-rowel, fig. 19) we find an extraordinary development of this intermediate skeleton,—which so completely envelops the original rotalian shell, that nothing can be seen of its chambers externally, save towards the termination of the last whorl of the spire, and which extends itself into clubshaped outgrowths that have no connexion with the chambered spire except through the canal system. There is no other recent Foraminifer at present known in which the “intermediate skeleton” and the “canal-system” attain such a remarkable development; and it was under the guidance of the structure of Calcarina, as previously elucidated by the writer’s microscopic inquiries, that Dr Dawson was first led to recognize the “canal-system” in Eozo&n canadense, and thus to determine its Foraminiferal character—as will be presently explained.

Another very interesting type which must be placed in the “globigerine” series on account of the coarseness of the perforations of its shell-wall, but whose spiral mode of growth differs entirely from that of ordinary Rotalians, is the Fusulina of the Carboniferous Limestone (fig. 20). This bears so strong a resemblance in form to the Alvcolina of the “Milioline” series (fig. 10), that it was for a long time associated with that type, although differing from it in the opening of its chambered interior by a single fissure along the middle of the lip, instead of by a row of pores. The interior, instead of being minutely divided into a number of separate chamberlets, is found to consist essentially of a symmetrical spire of simple chambers, each of which extends on either side into an “alar prolongation,” analogous to that of other spirally growing Foraminifera. But these alar prolongations, instead of overlapping the preceding whorls, as in Nummulites, are prolonged in the direction of the axis of the spire, those of each whorl projecting beyond those of the preceding, so that the shell is elongated with every addition to its diameter. These alar extensions are constricted at intervals, so as to form lirîêar series of partially divided chamberlets, and frequently take a somewhat irregular course; so that when the shell is traversed by sections (fig. 20) these reveal an aggregation of chamberlets (like those of the investing whorls of Nummulites, fig. 24), in which no definite arrangement can at first be traced.

Tire Family Nummulinida, of which the well-known fossil Num-muHte is a characteristic example, includes the greater part of the largest and most elaborately constructed of the “vitreous” Foram-iniiera. Various plans of growth prevail in this family; but its distinguishing characters consist in the completeness of the wall tluιt surrounds each segment of the body (the partitions between the chambers being double), in the density and fine tubulation of the shell-substance, and in the presence of an “intermediate skeleton” with a “canal-system” for its nutrition. This last, however, is altogether wanting in the smallest and more feebly developed examples of the group, such as iïonionina (19 in fig. 1), and is scarcely traceable in the small Pυlystυmella crispa(fi&\n fig. 1), one of themost common of British Foraminifera, though in the large Polystvmdla of tropical seas the canal-system presents a regular development not approached elsewhere. This is specially displayed by “internal casts” of this shell (fig. 21), that have been fortunately obtained by the decalcification of specimens in which the sarcodic contents of the chambers had been replaced by mineral deposit, so as to give an exact model of the original animal.

The Nummuline type is most characteristically represented at the present time by the genus Operculina, which is so intimately related to the true Nummulite by intermediate forms that the two types cannot be separated by any definite boundaries, notwithstanding the dissimilarity of their most characteristic specimens. This genus is represented in temperate seas by small and feeble examples; but it attains a much higher development in tropical seas, the largest existing Operculina, however, only attaining the size of the smaller fossil Nummulitcs. As the organization of Operculina affords the clue, not only to that of the great Nummuli tic series, which, at the commencement of the Tertiary epoch built up an immense mass of limestone that girdled a large part of the globe, but also to that of the far more ancient Eozoön, it will be described in some detail. The shell is a compressed nautiloid spire (fig. 22), the breadth of whose earlier convolutions increases in regular progression, but of which the last convolution (in full-grown specimens) usually flattens itself out like that of Peneroplis (5 in fig. 1). As a rule, the shell-wall of each whorl of the spiral completely invests all the preceding whorls; and each chamber-cavity (fig. 22, c, c)∙is continued from the margin towards the centre by two “alar prolongations,” one on either face of the spire (c', c'), which are filled during life by extensions of the sarcodic segments that occupy the successive chambers. The size and extent of these “alar prolongations” differ much in different varieties of Operculina, and often in different parts of the same shell,—being, as a rule, least marked in proportion as the spire flattens itself out. There is often no external indication of them, the successive whorls of the spire being visible from the centre to the margin; but in vertical sections the spiral lamina of each whorl is still seen to be continued over the whole of the preceding whorl, even to the centre of the spire, though it may adhere to it everywhere except near its margin. The chambers are separated by double septa, which are shown in transverse section at d, d ; these do not extend internally quite to the margin of the preceding whorl, but leave a fissured aperture, by which each chamber communicates with the one behind and before it, and the last chamber with the exterior, as seen at a"'. The “spiral lamina,” which encloses the chambers and their ‘ ‘ alar prolongations,” is perforated by minute closely-set tubuli of about τy⅜τ∏)th of an inch in diameter; the orifices of these are seen on the internal wall of the chambers to be disposed with great regularity, as in fig. 23; and they seem normally to run parallel to each other (fig. 24), so as to open with equal regularity on the external surface. But in their passage from the interior towards the exterior of the shell these tubuli sometimes approach and sometimes diverge from one another. so that the pseudopodia which pass through them issue forth in closely-set bundles, separated by intervening spaces of nontubular shell. These imperforate portions are harder than the porous shell, and often project as ridges or tubercles, forming a more or less regular “sculpturing” of the surface. They frequently correspond to the septa beneath, which are themeelves composed of non-tubular shell-substance, and are overlaid by ridges of the same vitreous imperforate material. Nothing can be more inconstant, however, than this sculpturing, even on different parts of the same shell; so that it cannot be accounted as of the least value as a specific character. The outer edge of the spire is bounded by a peculiar band, of different structure from the rest, which may be distinguished as the “marginal cord” (fig. 22, a, a). This band, instead of being perforated by minute parallel tubuli, is traversed by a set of larger canals, inosculating with each other, and forming part of the “canal-system,”—the peculiarity of its character being clearly shown in vertical sections of well-preserved fossil Ntιm-mulites (fig. 24, ⅛, b). The “canal-system” consists in the first place of a pair of “spiral canals,” which run along the edges of the marginal cord, communicating with each other through its system of inosculating passages; while from each of these there pass off into spaces left between the two layers of each septum (as shown at d', dfi, fig. 22) a series of “interseptal canals,” the distribution of which—marked out by causing them to imbibe coloured fluid—is seen in the septa e, e. The general arrangement of this canal-system will be better understood by reference to that of Polys-tomclla shown in its “internal cast” (fig. 21),—the position of the “spiral canals,” however, as well as the distribution of their branches, being veιy different.

The typical form of the Nummulite is lenticular (fig. 25, b), sometimes more nearly approaching the globular, whilst in other cases it is as compressed as that of Operculina,· —great differences of this kind presenting themselves between individuals, which, on account of their general conformity of structure, must be accounted specifically identical. It is among the compressed forms that the largest size is attained,—some of these measuring 4⅜ inches across, while the globose forms seldom much exceed an inch in diameter. The distinction which separates the typical Nummulües from the typical Opcrculinae consists in this, that in the former the earlier whorls are completely invested by the alar prolongations of the later,—the successive turns of the spiral lamina being separated overtheir whole surface from those internal and external to them by intervening spaces, as shown in fig. 26, so that the spire is but little, if at all, discernible on the surface. On the other hand, we never find the later whorls of true Nummulites flattening themselves out marginally, like those of the typical Operculinae; and there even seems reason to believe that when the spire has attained its full growth, it tends to close itself in. Curious differences are seen,in the course and arrangement of the “alar prolongations”; and it has been proposed to group the numerous modifications of the Nummulitic type in accordance with these differences. Thus, in some of these, the alar prolongations extend in a regular radial direction from the margin to the centre of each whorl of the spire, being separated by corresponding radial prolongations of the marginal septa. In other instances, again, they follow a sinuous course, the septa prolonged from those of successive chambers still remaining distinct from one another. From these, again, we pass to a group in which the septa inosculate, so as to break up τhe a]ar prolongations into subdivisions, the partitions between which (as seen in tig. 26) show themselves in vertical sections in far greater numbers than the proper septa.

And by a further increase of this subdivision, a complete reticulation is formed between the successive whorls of the spiral lamina, by the complex inosculation of the septal prolongations. Now, although it would not be difficult to arrange a collection of Nummulites under a number of specific types founded on these characters, if account were only taken of the specimens showing the most strongly marked differences, yet when due attention is given to the intermediate forms, they are found to present such a transitional gradation as to make it impossible to draw any absolute differential lines between the numerous components of the series.—The canal system of Nιιmmulina bears a close resemblance to that of Opercu∙ Una; and it is sometimes brought into beautiful distinctness in fossil specimens by the infiltration of ferruginous or other fossilizing material. And sometimes fragmentary “internal easts” present themselves, which admirably display the distribution of parts of the system (fig. 27).

We find in the larger forms of the Nummuline type the same tendency to become “labyrinthic,” by the subdivision of the principal chambers into ‘ ‘ chamberlets, ’ ’ that we have seen in the Mill oline. Just as Pcnc∙ roplis is converted by such subdivision into a spiral Orbiculina, and this, again, by the early exchange of the spiral for the cyclical plan of growth, into the cyclical Orbitolite, so Operculina, without any other departure from the ordinary Nummuline type, becomes Heterostegina (fig. 28); whilst the substitution of the cyclical for the spiral plan of growth produces the discoidal Cycloclypeus (fig. 29), the largest existing Foraminifer yet discovered, its diameter sometimes reaching 2∣ inches. This is the recent representative of the very important fossil type Orbitoides, examples of which present themselves very abundantly in many localities in association with Nummulites (fig. 25, o), which they so closely resemble as to be easily mistaken for them. Some of them are very thin flattened disks, of the proportion shown in vertical section in fig. 30; while others have two or three times the proportionate thickness. Each disk has a central plane of chamberlets (figs. 31, 32, b, b) resembling that of Cycloclypeus, arranged with a general but not constant regularity in concentric, circles; but whilst in the recent type this central plane is enclosed above and below by successive lamellae of tubular shell-substance not separated from each other by any intervening spaces, the superposed lamellae of Orbitoides are composed of chamberlets of irregular form (figs. 31, 32, a, a), which are piled up, one upon another, communicating vertically by minute apertures in their shell-walls. This arrangement obviously corresponds with that of the most reticulate forms of Nummulites.

Another important link of affinity between Orbitoides and Cycloclypeus is furnished by the disposition of the canal-system, which, allowance being made for the cyclical plan of growth of the former, as contrasted with the spiral plan of the latter, is essentially the same in the two types. This, moreover, is beautifully shown in “internal casts” of Orbitoidcs found by Professor Ehrenberg in the Greensand; which, though fragmentary, display a canalsystem precisely resembling that which the writer had worked out in Cycloclypcus by the examination of sections of the shell.

It has been by the study of such “internal casts,” recent and fossil, taken in connexion with the microscopic appearances shown in thin sections of its calcareous layers, that the Foraminiferal nature of the Serpentine-limestone of Canada has been elucidated, of which some of the deepest beds of the Laurentian formation(theearliest series of stratified rocks at present known) are composed, and which has its parallel in certain beds that lie near the base of the “fundamental gneiss” of central Europe. In order that the evidence of the organic origin of this rock— a point of the highest palaeontological and petrological interest—may be properly understood, regard must be had to what is even now going on in the depths of the ocean.

The animals that form the enormous mass of globigerina ooze at present in course of deposit over vast areas of the sea-bottom increase and multiply by limited gemmation; that is, the size of each individual shell, which depends upon the number of segments of which it is composed, is restricted by the cessation of continuous gemmation after a definite number of segments has been produced. An indefinite extension of the type, however, is provided for by the detachment of further segments, which, increasing by gemmation, in their turn give origin to now shells. In the larger Foraminiferal types last described, on the other hand, continuous gemmation proceeds much further; and thus we may have in an Orbitolite, a Nummulite, or a C ycloclypeus i hundreds or even thousands of chambers, all formed by the segmental extension of the animal body from one “primordial segment.” Further, in Polytrema we find a rotaline shell extending itself by the continuous gemmation of the animal, without any definite limit either of size or shape,—its increase taking place by vertical as well as by horizontal gemmation, so that it develops itself into forms which are essentially zoophytic. Hence there is nothing in the nature of Foraminiferal organization in the least degree inconsistent with the idea that a shell essentially “Nummuline” in its character should extend itself indefinitely by the continuous gemmation of the animal that forms it, not merely over horizontal planes, but also in the vertical direction, so as to produce solid massive structures bearing astrong general resemblance to Coral growths.

Again, the dead shells of Foraminifera brought up from many parts of the sea-bottom are found to have their cavities filled with green or ochreous ferruginous silicates, which seem allied in composition to the “glauconite” of the Greensand formation; and these mineral deposits occupy not merely the chambers of the shell, but its canalsystem also; so that when the calcareous shells have been dissolved away by dilute acid (which does not act on their contents), internal casts are obtained, which are perfect models, not only of the soft sarcodic segmented body of the animal, but also of its extensions into the canal-system that traverses the substance of the intermediate skeleton (figs. 21, 27). Yet further, this mineral deposit sometimes penetrates the minute tubuli of the shell itself; so that the surface of the internal cast of each chamber is beset with little points which represent the pseudopodia that extended themselves into those tubuli from each sarcodic .segment. There can be no reasonable doubt that these “internal casts” are formed by a process of chemical “substitution,”—the animal body, in the progress of its decay, being replaced, particle by particle, by ferruginous silicates precipitated from sea-water by the liberation of ammonia. And the explanation of the fact that this replacement only occurs in particular localities (notably in the Aegean, over the Agulhas bank near the Cape of Good Hope, and on certain parts of the Australian coast) probably lies in some local peculiarity in the composition of the sea-water, which may not improbably be due to the discharge from submarine springs of water containing an unusual quantity of the materials of the deposit.

Now there is ample evidence that a similar process has taken place at various geological periods. For, as was first pointed out by Professor Ehrenberg, the green sands which occur in different formations from the Silurian to the Tertiary epoch (being especially characteristic of the earlier Cretaceous) consist very largely (though not exclusively) of the “internal casts” of Foraminifera,— as is shown by microscopic examination of their grains. Examples of such casts, which can be referred without the least difficulty to known Foraminiferal types, have been already given (figs. 17, 27). Hence there is no inherent improbability in such an occupation of the chamber-cavities, of the canalsystem, and even of the minute tubulation, of a still earlier Foraminiferal structure, formed by the indefinite extension of a Nummuline growth into coral-like masses. And as there is every reason to believe that the composition of ocean-water has varied greatly at different geological periods, and especially that it contained magnesian salts at earlier epochs in much larger quantity than at present, it might be expected that the silicates which replace the soft tissues of the animals of the earliest organisms should be essentially magnesian. This expectation has been singularly confirmed by the fact ascertained by Dr Sterry Hunt, that in certain Silurian Limestones from Wales and New Brunswick, the segments of Crinoidal stems have the soft animal tissue, which originally filled the interspaces of their calcareous network, replaced by a silicate of alumina, iron, magnesia, and potass—intermediate between glauconite and serpentine. Now, the Serpentine-limestone that lies near the base of the Laurentiau formation in Canada is ordinarily composed of alternating layers of carbonate of lime (in the condition of calcite) and of silicate of magnesia (serpentine),—these layers being superposed upon one another with great general regularity (as shown in fig. 33), and frequently exceeding fifty of each kind in number. In some localities, however, the calcite is replaced by dolomite (magnesian limestone), while the serpentine is replaced either by loganite (a compound of silex, alumina, magnesia, and iron), or by some other magnesian silicate; but the alternation of calcareous and siliceous lamellae is just as regular in these cases as in the typical ophicalcite, and there is every probability that the dolomitic layers were originally formed as calcite, and subsequently metamorphosed by magnesian infiltration. The regularity of this alternation of calcareous and siliceous lamellae, which has no parallel in any undoubted mineral, taken in connexion with the resemblance of the entire formation (extending continuously over hundreds of square miles) to ancient coral reefs, having suggested to Sir William Logan its organic origin, a careful microscopic examination of specimens that seemed to have been least altered by metamorphic action was made at his instance by Dr Dawson of Montreal, with results that left him in no doubt either of the organic nature of the calcareous lamellae, or of the Foraminiferal affinities of the organism. These results were confirmed by the writer of this article, whose re-examination of the subject, to meet the objections raised from time to time against Dr Dawson’s conclusions, has only had the effect of strengthening his original conviction of their truth. And the following general sketch of the structure of Eozoön canadense is here presented with full confidence, as expressing, not merely his own vievzs, but those of the numerous eminent naturalists who have examined for themselves the evidentiary facts placed before them.

The calcareous lamellae of the Canadian Ophicalcite, which are always thickest near the base of the mass, are superposed one upon another so as to include between them a succession of “stories” of chambers (fig. 34, A 1 , A l , A a , A s ),−the chambers of each “story”

opening one into the other, as at a, a, like apartments ensuite, but being occasionally divided by complete septa, as at b, b, which are traversed by passages of communication between the chambers they separate. Each layer of shell consists of two finely-tubulated or ‘'Nummuline” lamellae, B, B, which form the boundaries of the chambers above and beneath, and of an intervening deposit of homogeneous shell-substance, c, c, which constitutes the “intermediate skeleton.” The amount of this varies considerably in different layers, while the thickness of the “proper wall” of the chambers (or “Nummuline lamella”) remains almost constant, the distinction between the two being just as marked (in well-preserved specimens) as it is in the recent Calcarina (fig. 19). The tubuli of the “Nummuline” lamellae are usually filled up (as in the Nummulitësof Nummulitic Limestone) by mineral infiltration, so as to present only a fibrous appearance in thin transparent sections; but it fortunately happens that, through its having escaped such infiltration, the tubulation (fig. 35, a, a) is occasionally as distinct as it is in recent Nummuline shells, bearing a strong resemblance in its occasional waviness (as at a', a ’ ) to that a crab’s claw. The “intermediate skeleton,” whenever it forms a thick layer, is penetrated by arborescent systems of canals (fig. 34, e, e), which are often distributed so extensively and so minutely through its substance as to leave very little of it without a branch. These canals (fig. 35, b, b) take their origin, not directly from the chambers, but from irregular lacunae or interspaces between the outside of the proper chamber-walls and the “intermediate skeleton,” exactly as in Calcarina, — the extensions of the sarcode-body which occupied them having apparently been formed by the coalescence of the ι>seudopodial filaments which had issued forth through the tubulated lamellae. It is to be remarked that the substance, not merely of the intermediate skeleton, but of the Nummuline layer, is traversed by oblique lines, indicating the cleavage-planes of calcite. This is what is constantly seen in fossilized calcareous organisms—-such as the shells and spines of Echinida, or the stems of Crinσidca- which retain their organic arrangement unchanged, and thus affords no basis whatever for the contention that these calcareous layers are purely mineral. On the other hand, the fact that the portions of the canal-system, shown in thin sections (fig. 35), continually cross the cleavage planes, instead of lying between them, furnishes astrong objection to the hypothesis that the appearances which have been interpreted as indicating a regular distribution of ramifying canals canhavebeen produced by mineral infiltration. Further, the distinct continuity of these cleavage-lines through the “Nummuline layer” (fig. 35, a, a) proves this layer to be essentially calcareous,— the layer of serpentine-fibres which is commonly found in its place after decalcification being a secondary deposit, formed in the manner to be presently described.

When a well-preserved fragment of Eozoön has been treated with dilute acid, so as to dissolve away the calcareous lamellae, we have an ‘ ‘ internal cast” in serpentine, which gives us a precise model of the sarcodic body by which the cavities of the calcareous structure were originally occupied. We see, in the first place (fig. 36), that each of the layers of serpentine forming the lower part of such a specimen shows more or less of a segmental arrangement,—being, in fact, made up by the coalescence of a number of minute serpentinous granules, such as are shown separately or but slightly coalescing in the upper part of the figure. This shows that there is not that difference between the regularly “lamellated” and the “acervuline” plans of growth which might at first sight be supposed,—the chambers having been separate in the latter, whilst in the former they constituted imperfectly subdivided galleries. In those wider spaces between the serpentine-layers, which were originally occupied by the thicker calcareous layers forming the “intermediate skeleton,” we find internal casts of the branching canal-system; and the development of this system is found, as in recent Foraminifera, to bear a constant relation to the amount of the secondary calcareous deposit. But further, in specimens in which the “Nummuline” layer was originally well preserved, and in which the decalcifying process has been carefully managed, that layer is represented by a thin white film covering the exposed surfaces of the segments; as is shown superficially over the upper part of fig. 36, and in section, along the margins of the serpentine lavera, in the lower. When this film is examined with a sufficient magnifying power, it is found to consist of extremely minute needle-like fibres of serpentine; which sometimes stand upright, parallel, and almost in contact with one another, like the fibres of asbestos, but which are frequently grouped in converging brush-like bundles, so as to be very close to each other in certain spots at the surface of the film, whilst widely separated in others,—thus indicating exactly the same irregularities in the grouping of the tubuli that (as already mentioned) we find in recent Nummulines. And it is not un frequently seen that where bundles of these fibres converge towards the surface, so that the pseudopodial threads they represent would have issued forth in clusters, the internal casts of the canal-system take their origin in such aggregations. We have here, in fact, in this most ancient of all fossils at present known, the most complete model wo possess of any extinct animal, extending even to its soft sarcodic threads of less than ∏>⅜τ∏½h of an inch in diameter,—this model being conformable in all essential particulars to the “internal casts” of existing Foraminifera which are at present in course of production on the sea-bottom.

Geographical Distribution.— Most of the Families of this group have a very wide geographical distribution,—this being especially the case with the smaller and simpler representatives of them that range over those vast areas in the deep oceanic basins, of which the bottom-temperature is kept down by the polar underflow. A striking resemblance has long been noted between the poor and feeble Foraminiferal fauna of shallow waters in colder-temperate seas, and that of great depths in tropical seas; and this similarity is now explained by the correspondence of the temperature to which these two faunae are subjected. The larger and most developed examples of existing Foraminifera, on the other hand, are limited to the shallower seas near tropical shores, or covering coral reefs where the bottom-temperature is comparatively high; or to partially enclosed seas, like the Mediterranean and Red Sea, which are cut off from the polar underflow by the shallowness of the straits which connect them with the oceanic basin. It is in such seas that we meet with the largest Orbiculinae, and the most complex Orbitolites and Alveolinae,— the first of these “imperforate” types being generally abundant in tropical shore-sands, the second in shallow dredgings along the Australian coast, the great barrier-reef, and the lagoons of “atolls” in the Coral Sea, while the third seems to attain its highest development in the Philippine Seas. So, again, among the “perforate” Lagenida, we find the “nodosarian” and “cristellarian” types attaining a very high development in the Mediterranean; the most complex forms of the “rotalian” type, including the zoophytic Polytrema, are only met with in tropical or sub-tropical seas; while, with the exception of small and modified Polystomellae and dwarfed Operculinae, there are no known representatives in the colder-temperate or polar seas either of the gigantic Cycloclypeus, or of the large Operculina and lleterostegina of the tropics. But while the Foraminiferal fauna thus obviously depends on an elevated temperature for the attainment of its highest development as regards the size and complexity of its individual members, the numerical multiplication of its lower forms (as is the case in many other groups) seems to be favoured by a much lower degree of warmth; so that we find the vast area of “globigerina-ooze” extending to the borders of the Polar seas. There, however, it ceases almost abruptly, the place of this calcareous deposit being taken by an accumulation of the siliceous skeletons of Radiolarians and Diatomaceae.

It is not a üttle curious, however, that recent researches should have disclosed the fact, that the existing Arenaceous Lituolida attain their highest development—in regard no less to size and complexity of structure than to number —on the deep sea-bottom,—the additions to our previous knowledge of the Foraminiferal fauna made by the dredgings of the “Porcupine,” the “Valorous,” and the “Challenger” having been far greater in this section than in either of the calcareous-shelled groups. And it would hence appear that an elevated temperature is not as essential to the high development of the Foraminifera which construct “tests” by gluing together grains of sand, as it. .is to that of the shell-forming types which separate the material of their “porcellanous” or “vitreous” skeletons from the seawater in which they live.

Geological Distribution.— There is no division of the Animal Kingdom whose range in time (so far as is at present known) can be compared with that of the Foraminifera. Looking, indeed, to the vast series of ages that must have been required for the deposit of that long succession of Upper Laurentian and Huronian rocks which intervenes between the Eozoic Limestone of the Lower Laurentians of Canada, and the lowest strata in which the most ancient representatives of the Palaeozoic fauna have as yet been found, it may even be said that all other fossils are modern by comparison. For the interval between the formation of the Canadian Fozoön and the period represented by the oldest fossils of the Lower Cambrian series seems undoubtedly to have been quite as great—geologically speaking—as that which intervened between the latter and the existing epoch, if not greater,—the “fundamental gneiss " of Sir Roderick Murchison, which represents in central Europe the Laurentians of Canada, and near the base of which is found the kindred Fozoön bavaricum, having a thickness estimated at 90,000 feet, and being overlaid by a great thickness of other non-fossiliferous rocks. Hence the determination of the organic origin of this Ophicalcite, and of its Foraminiferal affinities, which has been effected by the examination and comparison of parts of specimens so minute as to be scarcely visible to the naked eye, must be considered as one of the most remarkable results of microscopic research—fully equal in importance, when considered in all its bearings, to the discovery by Prof. Ehrenberg of the Foraminiferal origin of Chalk.

Indications of Eozoic structure have been found in various strata of uncertain age underlying the Silurians of North America, and also in some of the older rocks of the Scandinavian series; and there is no improbability in the idea that its existence may have been prolonged through the whole of that long period, commonly regarded as azoic, which has been designated by Prof. Dana as Archaean. In the earliest strata usually accounted fossiliferous there are found, alike in the old and new continents, a number of curious organisms, sometimes of considerable size, which have received the names Archaeocyathus, Stromatopora, and Receptaculites. The nature of these is still problematical, their internal structure not having yet been fully elucidated; but while it seems probable, on the one hand, that among the organisms whose similarity of external conformation has led to their association under these names, there may be several types of structure essentially different, there seems considerable reason to believe that some among them are really gigantic Foraminifera, presenting approximations to calcareous Sponges. The Limestones of the Silurian period have not been as yet minutely searched for the smaller forms of Foraminifera ; but green sands of Silurian age occur in various localities, the grains of which can be identified as “internal casts” of Foraminiferal shells.

It is in the Carboniferous Limestone that we first recognize a varied and abundant Foraminiferal fauna, which has recently been made the subject of special study by Mr H. B. Brady, whose very interesting results may be summed up as follows. (1) Of the “imperforate” or “porcellanous” Foraminifera no examples have been detected. (2) Of the “perforate” or “vitreous” series, on the other hand, each principal group is represented: the Lagenida very slightly; the Globigerinida by Textularia and various Rotaiïan types; while of the Nummulinida we find, not only three generic forms that are at the same time individually small and scantily diffused, but (in certain localities) such an accumulation of comparatively large shells of Fusulina (fig. 20), that they constitute almost the sole material of calcareous beds extending over large areas. (3) A large proportion of the foraminiferal types of this period belong to that “arenaceous” group which at present contains not merely the Lituolida, whose “tests” are entirely made up of cemented sand-grains (among which the Saccamina, fig. 5, a, b, is distinctly recognizable), but also a number of generic types more or less allied to the recent Valvulina, in which there is a “vitreous” shelly basis, more or less thickly incrusted by an arenaceous envelope. The “isomorphism” of these with true “nodo-sarines” and “rotalines” suggests the question whether they are not really in an evolutionary stage between the true sandy-tested and the completely calcareous-shelled types.

But there is a larger question even than this,—namely, whether those massive beds of Carboniferous Limestone whose texture is sub-crystalline, and in which scarcely any traces of organic structure are now discernible, do not owe their origin, like analogous beds of the Cretaceous formation, to Foraminiferal life. The general tendency of recent geological opinion has been to account for the absence of all traces of organic structure in such beds by the “metamorphism” they have undergone subsequently to their original deposition. Of the completeness with which such metamorphism may obliterate the evidence of organic origin in calcareous rocks it is impossible to have more “pregnant instances” than those afforded by the purely crystalline marble of Carrara, which is unquestionably a metamorphic Oolite, and the crystalline conversion of the Antrim Chalk in the neighbourhood of the basaltic outburst which forms the Giant’s Causeway. The abundance of Corals, however, in various beds of Carboniferous Limestone, accompanied by such accumulations of Brachiopods, Crinoids, &c., as might have been associated with them on coral reefs, taken in connexion with the fact that the substance of existing reef-building corals, when raised by upheaval, sometimes exhibits a metamorphism that causes it to bear a close resemblance to carboniferous limestone, has seemed to favour the belief that the azoic sub-crystalline beds of that formation had their origin in Coral growths. Against this, however, it may be urged that we have at the present time no continuity of Coral-growth over areas that are at all comparable to those which we find continuously covered with Carboniferous Limestone; that the real parallel to these is presented by the continuous beds of Chalk formerly deposited over vast marine areas, by those of the Nummulitic Limestone of the succeeding period, and by those of Globigerina-ooze still in progress of production; and that, if the tropical sea-bottom were now elevated into dry land, we should find over the deeper areas a continuous Foraminiferal deposit, interrupted in particular localities by upheaved reefs of Coral, whose slopes would be covered with calcareous-shelled Mollusks, Echinoderms, &c., bearing a general correspondence with the great Carboniferous Limestone formation.

Moreover, it has now come to be generally admitted that “metamorphism” is connected with mechanical disturbance, and especially with that “lateral thrust” which is the principal source of the plication and contortion of strata, and which must have given rise to the evolution of great heat. That such a change was extensively produced in the Carboniferous rocks of Great Britain at the end of the Palaeozoic period, when the horizontal and continuous Coal-measures were thus broken up into separate “basins,” bordered by intervening ridges formed by the uplifting of their subjacent limestone, is universally recognized. But, on the other hand, over the vast area of Russia that lies between the Baltic and the Ural mountains, there seems to have been no such force in action. Its strata are so nearly level that the determination of their order of superposition has been difficult. And there is such a remarkable absence of metamorphism even in those of Silurian age that we there find what are elsewhere slates represented by beds of clay, constituting the original form of that deposit which has elsewhere acquired the slaty character by subsequent metamorphism. Now, since it is here that we also find the most extensive development of FusulιnaΛimestonQ in the place of those sub-crystalline beds which elsewhere form the great bulk of the Carboniferous Limestone, there seems exactly the same reason for regarding such a Foraminiferal deposit as the original form of those beds. And this view derives remarkable confirmation from the phenomena presented by the Carboniferous Limestone of Ireland, which has been recently studied with great care by Prof. Hull. This formation extends over a very considerable area of the island,—constituting in its central portion an elevated plateau, whose nearly horizontal strata present no indication of lateral thrust, whilst along the margin of this area the calcareous strata have been elevated into ridges by thrust from the outside, with more or less of plication and contortion. Now, in these marginal ridges the traces of organic origin are scanty,—the presence of fossils, whether large or minute, being the exception and not the rule. In the level strata of the central plateau, on the other hand, the evidence of organic origin is almost everywhere complete; and whilst fossil Corals, Mollusks, Crinoids, &c., are abundant in particular beds, great masses of the limestone are found by microscopic examination to consist of little else than minute Foraminiferal shells. A very strong case, then, seems made out for the belief that Foraminiferal life has contributed very largely to the production of those vast beds of Carboniferous Limestone (often exceeding 1500 feet in thickness) in which scarcely any trace of organic origin can now be found,—this share bearing to that of the Corals, which are generally credited with the whole, somewhat of the same proportion that the Foraminiferal ooze of the deep-sea-bottom at the present time does to the Coral reefs of shallow waters, and the shells of Mollusks and Echinidans that live among them.

In the earlier Secondary rocks we do not find by any means the same evidence of abundant Foraminiferal life; but this is very probably to be accounted for by the conditions of their deposition. For during the Triassic period we find no representative of a deep oceanic calcareous deposit,—the only considerable limestone bed (the muschelkalk) being obviously composed of the remains of the more developed fauna of comparatively shallow water. It is interesting, however, to find certain clay beds of the New Red Sandstone yielding Foraminifera, chiefly of the Cristellarian type, which can be identified—not only generically and specifically, but even varietally—with forms common in the Italian Tertiaries, and still living in the Mediterranean. In many of the Liassic clays Foraminifera are found in great abundance; and here the “porcellanous” group first characteristically shows itself under one of its least modified types, the Spiroloculina. In the formation of many Oolitic Limestones it seems probable that Foraminifera had a considerable share. For while the material of many of the calcareous beds belonging to this formation was obviously furnished by debris of Corals, Echinoderms, and Mollusks, the nuclei of the component grains of the true Oolitic beds are so often found to be minute Foraminifera, that we seem justified in regarding those beds as having been formed by a sub-aerial metamorphosis of shore sands largely composed of the minute shells belonging to that group, like many tropical shore-sands of the present time.

It was by the comparative study of specimens of Chalk brought from different localities that Professor Ehrenberg was first led to the conclusion that this vast formation was mainly produced by the progressive accumulation and subsequent disintegration of the minute shells of various types of Foraminifera, especially Globigerina (fig. 14),— a conclusion to which Professor W. C. Williamson was independently led by his study of the “Levant mud,” a white chalk-like deposit at present in progress of formation on the comparatively shallow bottom of the eastern end of the Mediterranean. This conclusion has been fully borne out by the deep-sea soundings and dredgings since carried on; which have established the fact that large areas of the great ocean-basins are covered to an unknown thickness by a Foraminiferal ooze, which, when dried, corresponds in every particular with ordinary Chalk. And there is, moreover, very strong evidence that this deposit is not a repetition of the old Chalk formation, but an actual continuation of it over areas which have undergone no such upheaval as that which raised the chalk of Europe, Asia, and America into dry land. Not only the Chalk, but the subjacent Greensand appears to have originated in great degree in Foraminiferal life,—its glauconite grains being (in the localities in which they seem to have undergone least attrition) internal casts of easily-recognizable types of that group, formed by the process already described as still going on upon parts of the existing sea-bottom. Various larger types of all the principal groups of Foraminifera occur in different parts of the Cretaceous formation,—the “porcellanous” sub-order being now fully represented.

The highest development of the Foraminiferal type, as measured by the extraordinary abundance of its largest and most complex examples, seems to have been attained in the early Tertiary period, to which belongs the vast formation of Nummulitic Limestone, forming a band often of 1800 miles in breadth, and sometimes attaining several thousand feet in thickness, which may be traced eastwards from the Atlantic shores of Southern Europe and Northern Africa (the Pyramids being built of this rock, and on a terrace formed by it) through Western· Asia to Northern India and China, and likewise over large areas in North America—thus taking, to use the words of Sir Charles Lyell, a far more conspicuous part than any other Tertiary group in the solid framework of the earth’s crust. In some localities it seems to lie comformably upon Cretaceous strata, so as to establish the continuity between the latest Secondary deposits and the earliest Tertiaries formed in the deep sea. In some localities this Limestone is essentially composed of an aggregation of N^ummulites (including, however, the fossil remains of higher organisms), the spaces between the large and entire shells being filled in by minuter forms and by the debris of previous generations of the larger; whilst in other localities the Nummulites are replaced, wholly or in part, by Orbitoides and Orbitolites. In the Paris basin the Nummulitic Limestone is represented by the Calcaire grossier, which is for the most part of Foraminiferal origin. Its lower calcareous beds are chiefly Nummulitic; but in the middle part of the series we find the Milioline group predominating, some of its beds being chiefly composed of Orbitolites, whilst others (notably those of which a large part of Paris is built) are essentially made up by the aggregation of the smaller Miliolae. The calcareous sand of Grignon, which consists in great part (like many beds of the Oolitic formation) of shells comminuted by the action of the waves, contains a great abundance of Foraminifera,— among them the large and complex Dactylopora, which is only represented at the present time by a minute form of extreme simplicity. In various marine deposits of the middle and later Tertiary periods, especially those which form the slopes of the Apennines, Foraminifera are abundant; but the larger forms gradually give place to the smaller, and the Foraminiferal fauna progressively approximates more closely to that of the present time.

Altogether it would certainly be not too much to affirm that, so far as we are justified by positive evidence, no single group of the Animal Kingdom has contributed, or is at present contributing, so largely as the one of which a sketch has now been given to the formation of the crust of the earth,—byseparating carbonate of lime from its solution in sea water, and thus restoring to the solid form the vast quantity of that material which is continually being taken up in solution, and discharged into the oceanic basin, by the percolation of rain-water through the calcareous strata which have been elevated into dry land, which are thus undergoing continual degradation. And if the origin of the great part of the Carboniferous Limestone in Foraminiferal rather than in Coral life be accepted as probable, the share taken by Foraminiferal life in this process during the Palaeozoic period would appear to have been fully equalled by that which it took in the formation of the Chalk, and in the production of the Nummulitic Limestone, of more modem geological epochs. (w. b. c.)