PORTION OF TRANSVERSE SECTION OF REPTILE TOOTH OF ASTEROLEPIS
a. Nat. size.
b. Mag. twelve diameters.
Fig. 33.
A. Section of Jaw of Asterolepis.
c. Reptile tooth as shown in section.
a, b, & c. Row of ichthyic teeth in dermal plate of jaw.
B. Magnified representatives of ichthyic teeth, a and b, in A.
It seems truly wonderful, when one considers it, to what minute and obscure ramifications that variety of pattern which nature so loves to maintain is found to descend. It descends in the fishes, both recent and extinct, to even the microscopic structure of their teeth; and we find, in consequence, not less variety of figure in the sliced fragments of the teeth of the ichthyolites of a single formation, than in the carved blocks of an extensive calico print-yard. Each species has its own distinct pattern, as if, in all the individuals of which it consisted, the same block had been employed to stamp it; and each genus its own general type of pattern, as if the same radical idea, variously altered and modified, had been wrought upon in all. In the Dendrodic (Cœlacanth?) family, for instance, it is the radical type, that from a central nave there should radiate, spoke-like, a number of arborescent branches; but in the several genera and species of the family, the branches belong, if I may so express myself, to different shrubs, and present dissimilar outlines. It has appeared to me, that at least a presumption against the transmutation of species might be based on those inherent peculiarities of structure which are thus found to pervade the entire texture of the framework of animals. If we find erections differing from one another merely in external form, we have no difficulty in conceiving how, by additions and alterations, they might be brought to exhibit a perfect uniformity of plan and aspect: transmutation,—development,—progression,—(if one may use such terms,)—seem possible in such circumstances. But if the buildings differ from each other, not only in external form, but also in every brick and beam, bolt and nail, no mere scheme of external alteration could ever induce a real resemblance. Every brick would have to be taken down, and every beam and bolt removed. The problem could not be wrought by the remodelling of an old house: the only mode of solving it would be by the erection of a new one.