so found. On the whole, however, the fossil botanist looks to characters, other than those which are microscopical, for the discrimination of his specimens.

Animals. With few exceptions it is the hard parts of animals which are alone preserved in the fossil state. The exceptions, however, are instructive and lead us to expect further evidence of the same kind. Thus we have hair in good preservation, as in the case of the Siberian mammoth and rhinoceros, and in that of the fossil bones of Escholtz Bay, which have lost but little of their animal matter and which are dug up accompanied by hair. We have feathers of birds which have left very accurate traces in the remarkable fossil from the lithographic slate of Solenhofen, recently described by Professor Owen and by him called Archaeopteryx longicaudata. The firm integument of Ichthyosauri is often. evident, showing to what we are indebted for the wonderful state of preservation in which we find their skeletons.

The scales of fishes and reptiles are in many cases valuable as serving to indicate the affinities of the animal which once -possessed them. The microscopic examination of "ganoid" scales shews that they are composed internally of bone and externally of enamel; and it also exhibits the presence of lacunæ, canaliculi and Haversian canals as in ordinary bone. The preservation of the vast numbers of ganoid dermal skeletons is due to the large amount of earthy matter contained in them.

When we come to bone the microscope again renders great assistance, although it is in most cases subsidiary to the more important investigation founded upon the outward form and size of the specimens. It may, however, be remarked that "in birds the Haversian canals are more numerous and "smaller than in the mammalia, and frequently run in a "direction at right angles to the shaft; the lacunæ are also "smaller and more numerous. In reptiles the Haversian.

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"canals are few and very large; the lacunæ and the canali"culi are also very large, and the latter very numerous. In "fishes the structure is more irregular; there are no con"centric lamine; the Haversian canals are sometimes absent, "at others very large and numerous, frequently the lacunæ "are absent, while the canaliculi are unusually long and elegantly wavy and branched.” Thus we have a means, which we may venture to consider trustworthy, of discovering the affinities of vertebrated animals, especially when we have once established the class to which they belong. We may, for instance, infer the sauroid relationship of a fish or the batrachian character of a reptile from data furnished by microscopic examination. Thus Professor Quekett examined certain bones found by Dr. Falconer in the North of India, and pronounced them to be certainly reptilian and probably chelonian; this induced Dr. Falconer to conclude that they were the toe bones of the colossal tortoise, twenty feet long (Colossochelys atlas) of which he had previously found the carapace in the Sewalik hills. Again, some fragments of bone which were found in a chalk pit and were referred by Professor Owen to the class of birds, on examination by the microscope indicated reptilian affinities; and it was thus shewn that they might safely be ascribed to one of the great flying lizards of the secondary rocks, the Pterodactyls.

In the teeth of vertebrata we have many interesting differences of structure, discernable only by the microscope. I need not remark that one of the most important Palæontological characters of teeth is the manner in which they are fixed to the jaw; but beyond this we find that in many fossil ganoid fishes a labyrinthic structure is apparent, the external layer of cement converging by numerous convoluted folds towards the central cavity of the tooth. The genus Rhizodus was originally founded upon teeth from the Devonian and Carboniferous formations which possessed this character. The teeth of the

Labyrinthodon of Warwickshire and of the Mastodonsaurus of Wirtemberg shew this structure in a most remarkable degree; and the inference was drawn that, if these animals were reptilian, they would probably turn out to be related to the class of fishes; in some members of which we find the same structure of the tooth. The conclusion was borne out by the subsequent discovery and examination of other portions of the skeleton, indicating that the Labyrinthodon or Mastodonsaurus was Batrachian in its characters. Again,—“a rock"formation extends over many parts of Russia, whose mineral "characters might justify its being likened either to the old "or to the new red sandstone of this country, and whose posi

tion, relatively to the other strata, is such that there is great "difficulty in obtaining evidence from the usual sources as to "its place in the series. Hence, the only hope of settling "this question, (which was one of great practical importance, "since if the formation were new red, coal might be expected to “underlie it, whilst if old red, no reasonable hope of coal could "be entertained,) lay in the determination of the organic "remains which this stratum might yield; but unfortunately "these were few and fragmentary, consisting chiefly of teeth, "which are seldom perfectly preserved. From the gigantic size "of these teeth, together with their form, it was at first inferred "that they belonged to Saurian reptiles, in which case the "sandstone must have been considered as [probably] new red; "but microscopic examination of their intimate structure "unmistakeably proved them to belong to a genus of fishes "(Dendrodus) which is exclusively Palæozoic, and thus "decided that the formation must be old red."-(Carpenter.) Another instance is furnished by certain teeth similar to those of the Cestracion or Port-Jackson shark, and referred to the genus Acrodus-they are found throughout the whole of the secondary rocks. From their peculiar form they are called by quarrymen "fossil leeches," and the older fossilists regarded

them as petrified Vermes; but the structure, as shewn by the microscope, is closely similar to that of the teeth of Cestracion. (See Owen's Odontography.)

Passing to the Invertebrata we find microscopic characters of great importance in some of the divisions of the Mollusca. In many of the Cephalopoda there is an internal shell-the "cuttle-fish bone," which exhibits a very beautiful and remarkable structure. The outer shelly portion of this body consists of horny layers alternating with calcified layers, in which last may be seen a hexagonal arrangement like that present in the hinge tooth of Mya arenaria. The soft friable substance that occupies the hollow of this boat-shaped shell is formed of a number of delicate plates, running across it from one side to the other in parallel directions, having the appearance of millions of microscopic pillars. The shell thus becomes sufficiently light to float in water, and by its buoyancy assists in the motion of the animal. Most of the fossil cuttle fishes, however, are those which, like the Nautilus and Ammonite, possess external shell, having much the same structure that we find in bivalves. In some of the oldest fossil genera, actinoceras, gyroceras and phragmoceras, the siphuncle, or passage connecting the different chambers, is large, and contains in its centre a smaller tube, the space between the two being filled up with radiating plates, like the lamella of a coral. Another point of interest in connection with Cephalopoda is the fact that the Ammonites closed their shells by a horny or shelly operculum. In the round-backed Ammonites the operculum is shelly, and in its internal structure it resembles the cancellated tissue of bones.

The shell of the Brachiopoda is so characteristic that the examination of a minute fragment is sufficient to determine the class. According to Dr. Carpenter it consists of flattened prisms of considerable length arranged parallel to each other with great regularity, and obliquely to the surfaces of the

shell. Besides this, in most brachiopoda the shell is traversed by canals from one surface to the other, nearly vertically, and occurring regularly, the distance and size of the perforations varying with the species.

It may be well to notice here, that the structure of shell in specimens from old formations, is often made out only with difficulty. Carbonate of lime, whatever be its original form, shews a strong tendency to pass into a crystalline condition by a change in molecular arrangement. Thus in fossil crinoids we often discover that although the outward form of the animal is preserved, yet it breaks up without difficulty into fragments, having the characteristic rhombohedral fracture of calcareous spar. We have a ready explanation of this phenomenon in the power which water possesses, when containing carbonic acid gas, of dissolving carbonate of lime; and of re-depositing it again in the crystalline condition, when the carbonic acid escapes from solution. Incrustations of carbonate of lime due to this cause and found in conduit pipes, shew crystalline structure in a very marked degree. We are not surprised, therefore, to find that a similar effect has been produced in old fossil shells, whether of mollusca or of other classes of animals, if composed of carbonate of lime.

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The shell of Echinoderms is highly characteristic, being composed of a network of calcareous matter more or less regular, and familiar to microscopic observers. The plates are often furnished with calcareous appendages, tubercles, spines, hooks, anchors," etc., all forming exceedingly interesting objects. Count Münster has figured the microscopic plates, apparently of a Holothuria, from the chalk of Warminster; and the anchor of a Synapta from a still older formation, the upper oolite of Bavaria. "Microscopic observers will doubtless meet with many such detached "plates and spines, when searching for Polycystineæ and

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