Page:Popular Science Monthly Volume 43.djvu/504

488 of these blind cave-animals can be accounted for only by supposing that their remote ancestors began making excursions into the cave, and, finding it profitable, extended them, generation after generation, further in: undergoing the required adaptations little by little.

I turn now to Dr. Romanes. He says that I do not understand Weismann; and that the cause of degeneration to which he gives the name of "Panmixia" is not the continued selection of the smaller variations. Let us see what are Weismann's words,

"The complete disappearance of a rudimentary organ can only take place by the operation of natural selection; this principle will lead to its elimination, inasmuch as the disappearing structure takes the place and the nutriment of other useful and important organs" (Essays upon Heredity, p. 88).

"Those fluctuations on either side of the average which we call myopia and hypermetropia, occur in the same manner, and are due to the same causes, as those which operate in producing degeneration in the eyes of cave-dwelling animals" (lb., p. 89).

Here, then, are two propositions: (1) "Fluctuations on either side of the average" "operate in producing degeneration in the eyes of cave-dwelling animals." (2) "A rudimentary organ" is removed "by the operation of natural selection." Why are "fluctuations on either side of the average" named, unless it is that natural selection takes advantage of them by preserving the smaller variations? If this is not meant the use of the expression is meaningless. Yet Dr. Romanes agrees with Weismann in regarding the "degenerated eye of the Proteus as a good example of the disappearance of a complex and useless structure by Panmixia." So that Panmixia is clearly identified with the selection of the smaller variations; and for the reason that economy of nutrition is so achieved. Where, then, is the misunderstanding? That my interpretation is correct I have further reason for holding; namely, that it is the one given by Weismann's adherent. Prof. Lankester, in Nature, March 27, 1890 (pp. 487, 488). But while I can not admit my failure to understand Weismann, I confess that I do not understand Dr. Romanes. How, when natural selection, direct or reversed, is set aside, the mere cessation of selection should cause decrease of an organ irrespective of the direct effects of disuse, I am unable to see. Clearer conceptions of these matters would be reached if, instead of thinking in abstract terms, the physiological processes concerned were brought into the foreground. Beyond the production of changes in the sizes of parts by the selection of fortuitously arising variations, I can see but one other cause for the production of them—the