a centre like spokes from the nave of a wheel; and their arborescent aspect suggested to the Professor the name Dendrodus. It seems truly wonderful, when one but considers it, to what minute and obscure ramifications the variety of pattern, specific and generic, which nature so loves to preserve, is found to descend. We see great diversity of mode and style in the architecture of a city built of brick; but while the houses are different, the bricks are always the same. It is not so in nature. The bricks are as dissimilar as the houses. We find, for instance, those differences, specific and generic, that obtain among fishes, both recent and extinct, descending to even the microscopic structure of their teeth. There is more variety of pattern,--in most cases of very elegant pattern,--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; each genus has its own general _type_ of pattern, as if the same inventive idea, variously altered and modified, had been wrought upon in all. In the genus Dendrodus, for instance, it is the generic type, that from a central nave there should radiate, spoke-like, a number of leafy branches; but in the several species, the branches, if I may so express myself, belong to different shrubs, and present dissimilar outlines. There are no repetitions of earlier patterns to be found among the generically different ichthyolites of other formations. We see in the world of fashion old modes of ornament continually reviving: the range of invention seems limited; and we find it revolving, in consequence, in an irregular, ever-returning cycle. But Infinite resource did not need to travel in a circle, and so we find no return or doublings in its course. It has appeared to me, that an argument against the transmutation of species, were any such needed, might be founded on those inherent peculiarities of structure that are ascertained thus to pervade the entire texture of the framework of animals. If we find one building differing from another merely in external form, we have no difficulty in conceiving how, by additions and alterations, they might be made to present a uniform appearance; 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 can induce a real resemblance. Every brick must be taken down, and every beam and belt removed. The problem cannot be wrought by the remodelling of an old house: there is no other mode of solving it save by the erection of a new one.