are not differences relating to the life-characters, but merely to the physical forms in which life manifests itself.
As we know of no simpler organisms than these, and can not conceive that life could manifest itself in any simpler forms, we must regard them as the primordial animals—the progenitors of the animal kingdom.
The conclusion which we reach, then, is that not only all man's distinctively human qualities came to him by inheritance, but also all his purely animal qualities. The former came from human ancestors, the latter from animal ancestors. And as with the former, so with the latter; the more specific came from ancestors less remote, the more general from ancestors more remote. The most general, the absolutely fundamental and essential, came from the primordial living beings.
The animals of the first life-period were succeeded by others which, as we have seen, possessed not only the physiological characters of the primordial organisms, but also certain anatomical characters not received by inheritance, enabling them to carry out the physiological processes more perfectly. If for the sake of simplicity we consider the animals of the first and second life-periods to be those which we have already designated as the lowest and the lower animals respectively, then the latter received by inheritance from the former their functions of nutrition and reproduction, and acquired the special organs of alimentation and reproduction by which these functions were the better carried on. The question whence these new characters came need form no part of our present inquiry. For our purpose it will be sufficient to say that they resulted from external causes, it being understood that it is not intended to preclude the idea of the agencies in question being natural causes. The fact here to be set forth is that these animals of the second life-period transmitted, by the law of heredity, these characters that first appeared in them, along with those which they had received by inheritance, to their descendants. It is not to be supposed, of course, that the characters were preserved unmodified as to details, but only that their general nature, both as to structure and use, were retained. The animals of the third life-period—which we may consider those we have called the higher animals—therefore possessed at the outset all the characters of the first, together with those that were peculiar to the second. They, in their turn, under the influence of external causes, came to possess new characters—a vertebral column, four-chambered heart, etc.—while those which they had received by inheritance from their forerunners of the second period attained in them a higher development; in their turn, too, they transmitted their advanced organization to the succeeding order of beings—that is, to the human race. This
