NATURAL SELECTION 271 



very serious preliminary difficulty. In discussing this we con- 

 centrate our attention on the question of the loss or reduction 

 of the eyes in these animals. That other modifications are 

 found is obvious ; but the study of their origin is far less fully 

 documented and scarcely admits of a serious discussion. 



The difficulty encountered in discussing the loss or atrophy 

 of the eyes is that emphasised by Cucnot (1921, p. 485) and 

 Racovitza (1907, p. 450 and foil.). These authors maintain 

 that all the evidence suggests that the blindness of cave animals 

 did not originate as a modification acquired (e.g. by selection) 

 by normal immigrants from the light which wandered into 

 caves. They assert that the blind occupants of caves were 

 ' lucifuges,' which were already losing 

 their sight and wandered ' voluntarily ' 

 into caves and survived there, as in 

 the environment best suited to them. 

 If this were true, of course, we would 

 have to look on the atrophy of the eyes 

 not as an adaptation to the caverni- 

 colous habit, but the latter as an adapt- 

 ation to the loss of eyes ! Cuenot (I.e.) 

 also points to the existence of animals 

 with normal eyes in caves, and reason- , Flu - 2 l-~ Le P todir " s ., h °: 



' 1 • 1 • henwarti Schmidt (bilphi- 



ably enough affirms that, to explain this dae). An Example of a 

 (as is usually done) by suggesting that highly evolved Cave- 



\ ' . . BEETLE WHICH IS NEVER- 



they are newcomers, is pure assumption, theless found in several 



It seems to US that it is fair tO SUS- Cavern-systems. Photo, 

 ... . . . T . W. H. T. Tarns. 



pend judgment on this question. It is 



not possible to resist Racovitza's and Cuenot's argument, even 

 if we suspect their anti-selectionist bias. It is to be noted that 

 Jeannel in his recent summary (1926) avoids discussing the 

 actual mode of origin of these modifications. 



B. Difficulties raised by the Natural Selection theory. 



It is necessary at the offset to remember that the large 

 body of specific and racial differentia that have been described 

 include a certain proportion that are merely the effect of 

 plastic responsiveness to the environment, and are not of a 

 fixed heredity. The adherent of Natural Selection may be 

 relieved of the necessity of explaining by his theory many 

 distinctions that are non-heritable (Robson, 1928, p. 186). 

 Thus it is quite evident from a perusal of a work like Pelseneer's 



