SO McCLUNG. 



pregnated eggs always males. This fact Dzierzon demonstrated 

 by observation in 1853, and the absence of spermatozoa from 

 the eggs which develop into drones has very recently been proven 

 in the laboratory of Weismann by the use of modern cytological 

 methods. 



A further proof, although inferential, is that afforded by 

 "true" twins, in which case it appears that the sex of the 

 two individuals is always the same. If sex were established at 

 the time of fertilization of the ovum, then sex would be shared 

 along with the other qualities possessed by the normal indi- 

 vidual that would have developed from the ovum under ordinary 

 conditions. In case sex were not established at the time of im- 

 pregnation, it would be natural to expect the two sexes to be 

 occasionally represented in one birth because of the inequality 

 of nutrition in the embryos or for other reasons. 



Sex, then, is determined sometimes by the act of fertilization 

 and can not be subsequently altered. But between this extreme 

 and the other of marked instability there may be found all de- 

 grees of response to environment. It must accordingly be 

 granted that there is no hard-and-fast rule about the determina- 

 tion of sex, but that specific conditions have to be taken into 

 account in each case. The objection that Geddes and Thompson 

 raise against the possibility of two forms of eggs, viz., that it is 

 a useless adaptation on account of the fact that subsequent con- 

 ditions may determine sex in some cases, is not a valid one in 

 general. Such may be the case in some instances, but such is 

 not the case in others. 



Finally, with respect to the evidence to be derived from 

 parthenogenesis, it should be remembered that we are here deal- 

 ing with a practical suppression of sexuality and it is to be ex- 

 pected that extensive modifications of the ordinary process will 

 follow. If the egg takes upon itself all the functions commonly 

 exercised by it in conjunction with the spermatozoon, it must be 

 that the determination of sex is included. This, in some in- 

 stances, is a final choice on the part of the ovum and ever after- 

 ward one sex only is produced by it ; again, however, it main- 

 tains a responsive attitude toward environments and gives rise to 

 the sex most needed by the species. It is to be hoped that the 



