the disposition of the internal organs. But, if this were ever so much greater, there would still remain something to explain and something of importance. This vertebrate has muscles, organs of senses, viscera like the various animals from which it is supposed to have proceeded. But there are, further, in it living substances of a special order, cartilage and bone, which are real chemical species. When, how, and under what circumstances did these substances appear which we find identical as to themselves in all vertebrates which no other existing animals possess? It is not enough to show us this animal type proceeding from that other, that organ developing itself or disappearing or changing place and relations. We want to be told through what internal chemical actions these organic compounds appeared; those clearly defined substances the presence of which establishes an absolute distinction between vertebrate animals and the worms or mollusks from which they are supposed to descend.
Just as the appearance of new chemical compounds hitherto unknown was the necessary condition of the formation of new organic types, so it seems proper to suppose that at the beginning life on our planet appertained only to amorphous masses, which, in a prodigious succession of ages, after incommensurable periods, in consequence of an intimate working in their substance, were succeeded by existences the contours and dimensions of which were gradually and progressively defined. The sense of this necessity, doubtless, haunted M. Haeckel's imagination when he supposed that the Bathybius was the primordial jelly whence all living beings were derived.
On the other hand, this idea of a simple beginning of life was too far lost sight of by M. F. A. Pouchet and the later champions of the doctrine of spontaneous generation. It is not shown that the question of heterogeneity, which was so exciting thirty years ago, can ever be answered. In any case, it can not be revived under the form which its latest defenders have given it. Their chief error, from which all the others have been derived, was in wishing to overshoot the mark, in seeking to create at the bottom of their matrass, not substance having life—a bit of sarcode or protoplasm—but a being having a definite form. In the modern idea of the necessities of life, form appears to us as an epiphenomenon resulting from infinitely numerous and infinitely progressive circumstances. To sum it all up, form is pre-eminently a hereditary characteristic. It can exist, we can only comprehend it as slowly acquired by a process of modeling a thousand and a thousand times secular. It was this form, this figure, that the partisans of spontaneous generation thought they brought forth in their apparatus! The objection we raise here, very curiously, was never made to them, and their theory was only ruined by
