had not its _Cestracion_,—a statement which could not be made regarding any other vertebrate family. In Agassiz’s “Tabular View of the Genealogy of Fishes,” the Cestracionts, and they only, sweep across the entire geologic scale. And, as shown in the figure, the mouth in this ancient family, instead of opening, as in the ordinary sharks, under the middle of the head, to expose them to the suspicion of being creatures of low and embryonic character, opened in a broad, honest-looking muzzle, very much resembling that of the hog. The mouths of the most ancient Placoids of which we know any thing, _did not_, I reiterate, _open under their heads_. But why introduce the element of embryonic progress into this question at all? It is not a question of embryonic progress. The very legerdemain of the sophist—the juggling by which he substitutes his white balls for black, or converts his pigeons into crows—consists in the art of attaching the conclusions founded on the facts or conditions of one subject, to some other subject essentially distinct in its nature. Gestation is not creation. The history of the young of animals in their embryonic state is simply the history of the fœtal young; just as the history of insect transformation, in which it has been held by good men, but weak reasoners, that there exists direct evidence of the doctrine of the resurrection, is the history of insect transformation, and of nothing else. True, the human mind is so constituted that it converts all nature into a storehouse of comparisons and analogies; and this fact of the metamorphosis of the creeping caterpillar, after first passing through an intermediate period of apparent death as an inert aurelia, into a winged image, seemed to have seized on the human fancy at a very early age, as wonderfully illustrative of life, death, and the future state. The Egyptians wrapped up the bodies of their dead in the chrysalis form, so that a mummy, in their apprehension, was simply a human pupa, waiting the period of its enlargement; and the Greeks had but one word in their language for butterfly and the soul. But not the less true is it, notwithstanding, that the facts of insect transformation furnish no legitimate key to the totally distinct facts of a resurrection of the body, and of a life after death. And on what principle, then, are we to trace the origin of past dynasties in the changes of the fœtus if not the rise of the future dynasty in the transformations of the caterpillar? “These [embryonic] characters [that of the heterocercal tail, and of the mouth of the ordinary shark type] are essential and important,” remarks the author of the “Vestiges,” “whatever the Edinburgh Reviewer may say to the contrary;—they are the characters which, above all, I am chiefly concerned in looking to, for they are the features of embryonic progress, and embryonic progress is the grand key to the theory of development.” Yes; the grand key to the theory of _fœtal_ development; for embryonic