scarce any of this earth: it is a framework of indurated animal matter, elastic, semi-transparent, yielding easily to the knife, and, like all mere animal substances, inevitably subject to decay. I have seen the huge cartilaginous skeleton of a shark lost in a mass of putrefaction in less than a fortnight. I have found the minutest bones of the osseous ichthyolites of the Lias entire after the lapse of unnumbered centuries. The two series do not seem to precede or follow one another in any such natural sequence as that in which the great classes of the animal kingdom are arranged. The mammifer takes precedence of the bird, the bird of the reptile, the reptile of the fish; there is progression in the scale; the arrangement of the classes is consecutive, not parallel. But in this great division there is no such progression; the osseous fish takes no precedence of the cartilaginous fish, or the cartilaginous, as a series, of the osseous. The arrangement is parallel, not consecutive; but the parallelism, if I may so express myself, seems to be that of a longer with a shorter line ;-the cartilaginous fishes, though much less numerous in their orders and families than the other, stretch farther along the scale in opposite directions, at once rising higher and sinking lower than the osseous fishes. The cartilaginous order of the sturgeons, a roe-depositing tribe, devoid alike of affection for their young, or of those attachments which give the wild beasts of the forest partners in their dens, may be regarded as fully abreast of by much the greater part of the osseous fishes in both their instincts and their organization. The family of the sharks, on the other hand, and some of the rays, rise higher, as if to connect the class of fish with the class immediately above it,-that of reptiles. Many of them are viviparous, like the mammalia,-attached, it is said, to their young, and fully equal to even birds in the strength of their connubial attachments. The male, in some instances, has been known to pine away and die when deprived of his female companion.* But then, on the other hand, the cartilaginous fishes in some of their tribes sink as low beneath the osseous as they rise above them in others. The suckers, for instance, a cartilaginous family, are the mcst imperfect of all vertebrated animals; some of them want even the sense of sight; they seem mere worms furnished with fins and gills, and were so classed by Linnæus; but though now ascertained to be in reality fishes, they must be regarded as the lowest link in the scale,-as connecting the class with the class Vermes, just as the superior cartilaginous * Some of the osseous fishes are also viviparous, the "viviparous blenny," for instance. The evidence from which the supposed affection of the higher fishes for their offspring has been inferred, is, I am afraid, of a somewhat equivocal character. The love of the sow for her litter hovers at times between that of the parent and that of the epicure; nor have we proof enough, in the present state of ichthyological knowledge, to conclude to which side the parental love of the fish inclines. The connubial affections of some of the higher families seem better established. Of a pair of gigantic rays (Cephaloptera giorna) taken in the Mediterranean, and described by Risso, the female was captured by some fishermen; and the male continued constantly about the boat, as if bewailing the fate of his companion, and was then found floating dead. (See Wilson's article ICHTHYOLOGY, Encyc. Brit. seventh edit.) fishes may be regarded as connecting it with the class Reptilia. Between the osseous and the cartilaginous fishes there exist some very striking dissimilarities. The skull of the osseous fish is divided into a greater number of distinct bones, and possesses more moveable parts, than the skulls of mammiferous animals ; the skull of the cartilaginous fish, on the contrary, consists of but a single piece, without joint or suture. There is another marked distinction. The bony fish, if it approaches in form to that general type which we recognise amid all the varieties of the class as proper to fishes, and to which in all their families nature is continually inclining, will be found to have a tail branching out, as in the perch and herring, from the bone in which the vertebral column terminates; whereas the cartilaginous fish, if it also approach the general type, will be found to have a tail formed, as in the sturgeon and dog-fish, on both sides of the lower portion of the spine, but developed much more largely on the under than on the upper side. In some instances it is wanting on the upper side altogether. may be as impossible to assign reasons for such relations as for those which exist between the digestive organs and the hoofs of the ruminant animals; but it is of importance that they should be noted.* It may be remarked, further, that the great bulk of It * Dr Buckland, in his Bridgewater Treatise, assigns satisfactory reasons for this construction of tail in sharks and sturgeons. Of the fishes of these two orders, he states," the former perform the office of scavingers, to clear the water of impurities, and have no teeth, but feed, by means of a soft fishes whose skeletons consist of cartilage, have yet an ability of secreting the calcareous earth which composes bone, and that they are furnished with bony coverings, either partial or entire. Their bones lie outside. The thorn-back derives its name from the multitudinous hooks and spikes of bone that bristle over its body; the head, back, and operculum of the sturgeon are covered with bony plates; the thorns and prickles of the shark are composed of the same material. The framework within is a framework of mere animal matter; but it was no lack of the osseous ingredient that led to the arrangement,—an arrangement which we can alone refer to the will of that all-potent Creator, who can transpose his materials at pleasure, without interfering with the perfection of his work. It is a curious enough circumstance, that some of the osseous fishes, as if entirely to reverse the condition of the cartilaginous ones, are partially covered with plates of cartilage. They are bone within and cartilage without, just as others are bone without and cartilage within. But how apply all this to the Geology of the Old Red Sandstone? Very directly. The ichthyolites of leather-like mouth, capable of protrusion and contraction, on putrid vegetables and animal substances at the bottom; and hence they have constantly to keep their bodies in an inclined position. The sharks employ their tail in another peculiar manner, to turn their body, in order to bring their mouth, which is placed downwards beneath the head, into contact with their prey. We find an important provision in every animal to give a position of ease and activity to the head during the operation of feeding." (Bridgewater Treatise, p. 279, vol. i. first edit.) E this ancient formation hold, as has been said, an intermediate place, unoccupied among present existences, between the two series, and in some respects resemble the osseous, and in some the cartilaginous tribes. The fact reminds one of Dr Johnson's shrewd objection to the theory embraced by Soame Jenyns in his Free Inquiry, and which was the theory also of Pope and Bolingbroke. The metaphysician held with the poet and his friend, that there exists a vast and finely-graduated chain of being from Infinity to nonentity-from God to nothing; and that to strike out a single link would be to mar the perfection of the whole.* The moralist demonstrated, on the contrary, that this chain, in the very nature of things, must be incomplete at both ends,-that between that which does, and that which does not exist, there must be an infinite difference, that the chain, therefore, cannot lay hold on nothing. He showed, further, that between the greatest of finite existences * "See, through this air, this ocean, and this earth, Where, one step broken, the great scale's destroyed: (Essay on Man.) |