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, Cuénot, 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 sad 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 Cuénot, 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 
