488 THE POPULAR SCIENCE MONTHLY. 



of these blind cave-animals can be accounted for only by suppos- 

 ing 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 under- 

 stand 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, inas- 

 much 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 aDd 

 hypermetropia, occur in the same manner, and are due to the same causes, as 

 those which operate in producing degeneration iD the eyes of cave-dwelling ani- 

 mals" (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 expres- 

 sion 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 Pan- 

 mixia." * So that Panmixia is clearly identified with the selec- 

 tion of the smaller variations ; and for the reason that economy 

 of nutrition is so achieved. Where, then, is the misunderstand- 

 ing ? That my interpretation is correct I have further reason for 

 holding ; namely, that it is the one given by Weismann's adher- 

 ent, Prof. Lankester, in Nature, March 27, 1890 (pp. 487, 488). But 

 while I can not admit my failure to understand Weismann, I con- 

 fess 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 ab- 

 stract 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 



* Contemporary Review, April, 1893, p. 509. 



