Page:Popular Science Monthly Volume 16.djvu/120

 other. . . . That some such resemblance should, in fact, be found to prevail is only what might naturally be expected, considering that each full-grown individual is itself the result of a process of gradual development from a sizeless and shapeless germ, in which development all its organs equally participate," etc. Here, again, we encounter the same argument from "necessity" that has just been considered; and here, again, it is no less preposterous than it was in its previous connection. For to an embryologist nothing could appear more ridiculous than the statement that "in such a case of gradual development it follows, almost as a matter of course, that both the entire animal and all its component members should, in their advance to maturity from a mere punctum saliens, exhibit some faint resemblance" to other and allied animals. As a matter of fact, the resemblance is never "faint" but profound, affecting all the structures which constitute the essential framework of the organism. The kind of resemblance on which the reviewer would appear inclined to place most reliance would be a superficial resemblance of specific details. But although even this is supplied by many facts—such as the hair on the unborn child, clothing the body except on the palms of the hands and the soles of the feet, which are also denuded in apes—it is not of so deep a significance to a philosophical mind as are the deeper resemblances of anatomical structure. Hence, even if the unborn young of a higher animal were, "at any stage of its development, identical with any of the lower animals," the fact would not speak so strongly in favor of its derivation from a lower form as does the fact of its passing through a whole series of changes, each stage of which refers, in some point of anatomical significance, to some stage in the existing grade of animal organizations. Actual identity is not what the theory of descent with modification would lead us to expect, seeing that, according to this theory, the comparable features usually refer to features that are derived from a common ancestor lower down in a branching stem of descent. In a family tree we may expect the constituent members to inherit in common some peculiarities possessed by their common ancestors, but we do not expect the personal appearance of all the individuals to be identical. Lastly, when we consider the enormous complexity of organisms, the marvel is how the more complicated, in attaining their higher complexity, mimic so closely the anatomical structures of the organisms lower in the scale of complexity. Far from its being "almost a matter of course," it is in the last degree astounding that a vertebrated animal, for instance, should begin its course of development by the same process of yolk-cleavage that occurs in the rest of the animal kingdom, that its first differentiation of body-layers should present the essential anatomical features of the body-layers that characterize the jelly-fish, and so on. In short, when any one at all acquainted with the facts of embryology regards them en masse, the last of all notions to enter his mind will be that they