Page:Popular Science Monthly Volume 77.djvu/306

300 these I may mention the very interesting papers by Griggs on juvenile kelps, Zeleny on the development and regeneration of serpulids, and Eigenmann on the blind vertebrates of North America.

Griggs especially criticizes the views of such critics of recapitulation as His, who holds that the reason why ontogeny seems to recapitulate phylogeny is because the developing organism must from physiological necessity pass from less to more complex stages, more or less resembling ancestral forms; and the views of Morgan, who holds that only embryonic stages of ancestors are repeated. This is the so-called "Repetition Theory." To both of these critics Griggs objects that they confuse physiology and morphology. "The recapitulation theory," he says, "has nothing to do with physiology; it is purely a matter of morphology."

On the first point, that the developmental stages are merely the physiologically necessary steps in the development of the adult organism, the conclusions of Eigenmann and Zeleny are of especial interest. Eigenmann shows that in the blind fish, Amblyopsis, the development of the foundations of the eye is normal, and is phylogenic, while the stages beyond the foundations are direct. Zeleny concludes that the ontogenesis of the opercula of serpulids is phylogenic, and recapitulates ancestral characters; but the regeneratory development of the organ is direct, and may be very different from the ontogenetic development. We may ask, therefore, if development takes a certain course only because that is the physiologically necessary way in which the individual or the organ must develop, why should a condition of perfect blindness, with almost total loss of all the eye structures, be attained only by the round-about method of first developing the foundations of a normal eye? Why, again, if there is any physiologically necessary course of development, should the serpulid be able to regenerate the opercula in a manner entirely different from their ontogenesis?

Hatschek, Hurst, Montgomery and others maintain that, if two individuals differ in the adult, they must also differ in the egg, and consequently must be different at all stages between. From this thesis they draw the conclusion that organisms can not recapitulate adult ancestral characters, because any change in the adult stage of an individual, causing it to be different from its parents, involves a change in the entire ontogeny—"the entire row of cells" from the egg to the adult. That there is some sort of change in the entire row of cells we grant; but that this change necessarily affects the morphology of the individual or of its organs, up to the adult stage, we do not grant. We have here again a confusion of morphology and physiology. The cell energies may indeed be changed; but unless a change in the cell energies inevitably necessitates a change in the morphology of all the cells or of all the organs which they compose, the argument of Montgomery proves nothing.