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Page:Popular Science Monthly Volume 57.djvu/412

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POPULAR SCIENCE MONTHLY.

force to germinal selection. This, however, would be changed were the effect of disuse admitted to affect the determinants, and this it seems Weismann has unconsciously admitted. So far we have considered germinal selection in the abstract only. All its suppositions are found to be but a house of cards when the actual conditions of degeneration are considered. We find that degeneration is not a horizontal process affecting all the parts of an organ alike, as Weismann presupposes, not even a process in the reverse order of phyletic development, but the more vital, most worked parts degenerate first with disuse and panmixia; the passive structures remain longest. The rate of degeneration is proportional to the past activity of the parts, and the statement that "passively functioning parts—-that is, parts which are not alterable during the individual life by function—by the same laws also degenerate when they become useless'* finds no basis in fact, and is an example of the inexact utterances abundant in the discussion of degeneration on which it is entirely unsafe to build lofty theoretical structures. As one example of the unequal degeneration we need only call attention to the scleral cartilages and the rest of the eye of Troglichthys rosæ.

All are agreed that natural selection alone is insufficient to explain all, if any, of the processes of degeneration. All either consciously or not admit the principle of panmixia, and all are now agreed that this process alone can not produce extensive degeneration. All are agreed that the important point is degeneration beyond the point reached by panmixia, the establishment of the degenerating process, whatever it may be, in the germ, or, in other words, the breaking of the power of heredity. It. is in the explanation of the latter that important differences of opinion exist.

Weismann attempts to explain the degeneration beyond the point which panmixia can reach by a process which not only is insufficient, even if all his premises are granted, to produce the desired result without the help of use transmission, but has as its result a horizontal degeneration which has no existence in fact.

Romanes supposed degeneration, beyond the point which may be reached by panmixia, to be the result of personal selection and the failure of the hereditary force. The former is not applicable to the species in question, and is denied by such an ardent Darwinist as Weismann to be applicable at all in accounting for degeneration. Moreover, the process as explained by Romanes would result in a horizontal degeneration which has no existence in fact. The second assumption, the failure of hereditary force, is not distinguishable, as Morgan has pointed out, from the effect of use transmission.

The struggle of parts in the organism has not affected the eye through the lack of room, since the space formerly occupied by the eye is now filled by fat and not by an actively functioning organ. It is not