THE DETERMINATION OF SEX. 113 



male egg. Hence, since the female element dominates in these ani- 

 mals when the two sexes meet, the individual must become a female. 

 Since therefore such an egg carries the male element in a recessive 

 form, this element may, if it becomes separated from its female asso- 

 ciate, give rise to a male. In this way the theoretical difficulty referred 

 to above is met. 



Let us follow out a little further the applications of this view. It 

 is probable in the honey-bee that all the eggs give off two polar bodies. 

 Consequently unfertilized eggs must produce pure males. If they 

 are fertilized by female spermatozoa they will give rise to females, 

 and, on the hypothesis, only female spermatozoa can enter male eggs. 



In rotifers and certain crustaceans only one polar body is given 

 off, but since this is the first polar body it does not involve the question 

 of sex. Consequently the parthenogenetic eggs in these forms are sex 

 hybrids. If at any time the conditions change so that one or the 

 other sex element dominates, males and females may arise. But why 

 the female element should dominate in some eggs and the male in others 

 is not explained, and thus we are in exactly the same predicament as 

 we were before Castle's hypothesis was proposed. 



One case of special difficulty should not pass unnoticed since Castle 

 has made an interesting suggestion that appears to clear up a difficulty, 

 provided the facts on which the conclusion rests are confirmed. The 

 eggs of the honey-bee extrude two polar bodies, as we have said, and 

 hence are purely male. It is assumed that these males must produce 

 spermatozoa that are female. This is a necessary assumption, because 

 the eggs of the bee having extruded their two polar bodies are purely 

 male, but become female after they are fertilized. Therefore the 

 spermatozoon must bring the female element into the egg. Castle 

 tries to meet this difficulty of the formation of female spermatozoa in 

 a purely male individual by reference to a recent observation of 

 Petrunkewitsch, namely, that the reproductive organ of the male 

 bee develops not from the egg itself, but from the second polar body 

 which fusing with one of the first pair reenters the egg. This second 

 polar body is, on Castle's theory, purely female, hence the spermatozoa 

 must be female. The ingenuity of the explanation is admirable, and 

 rescues the theory from a fatal objection, but of course even if Petrunke- 

 witsch 's results are accurate (and they are not above suspicion) it by 

 no means follows that the spermatozoa that come from the second polar 

 body are female, as Castle assumes. The facts in regard to the partheno- 

 genesis, and in regard to the special case of the bee, may possibly be 

 given a much simpler explanation than that which Castle applies to 

 them. For instance, if in certain insects the addition of the chromatin 

 material of a spermatozoon (or what amounts to the same thing the 

 chromatin contained in a polar body) determines that the egg shall 



VOL. LXIV. — 8. 



