Sex as an Adaptation 435 



male parthenogenesis, and if the theory of the equivalency 

 of spermatozoon and egg be correct, this is what should 

 occur. 



Quite recently, Cuenot, Beard, Castle, and Lenhossek have 

 contended that the differentiation of sex is the outcome of inter- 

 nal factors. They think that the view that sex is determined 

 by external agents is fundamentally erroneous. The fallacies 

 that have given rise to this conception, Castle points out, are, 

 first, that in animals that reproduce sometimes by partheno- 

 genesis and sometimes by fertilized eggs, the former process 

 is favored by good nutrition and the latter by poor nutrition. 

 This only means, in reality, Castle thinks, that parthenogenetic 

 reproduction is favored by external conditions, and this kind 

 of reproduction, he thinks, is a thing sui generis, and not 

 to be compared to the formation of more females in the 

 sexual forms of reproduction. There is no proof, how- 

 ever, that this is anything more than a superficial distinction, 

 and it ignores the fact that in ordinary cases the females 

 sometimes lay parthenogenetic eggs which differ, as far as we 

 can see, from eggs that are destined to be fertilized in no 

 important respect. More significant, it seems to me, is the 

 fact that only parthenogenetic females develop the following 

 spring from the fertilized eggs of the last generation of the 

 autumn series, whose origin is described to be due to lack 

 of food. We find, in the case of aphids, that unfertilized 

 parthenogenetic eggs and also fertilized eggs give rise to 

 females only, while a change in the amount of food causes 

 the parthenogenetic eggs to give rise both to males and to 

 females. This point is not, I think, fully met by Castle, for 

 even if the change in food does not, as he claims, cause only 

 one sex to appear, yet lack of food does seem to account for 

 the appearance of the males at least. 



The other fallacy, mentioned by Cuenot, is that the excess 

 of males that has been observed when the food supply is 

 limited is due to the early death of a larger percentage 



