THE DETERMINATION OF SEX. 109 



patent and touches such a fundamental point of Beard's theory that 

 it is more than surprising that he has said nothing about it. If the 

 female aphid develops from a female egg (the polar bodies of which 

 are on Beard's theory also female), we can understand why in the next 

 generation she must give rise to female eggs, but why should males 

 ever be again produced ? Since it has been established beyond question 

 that these parthenogenetic females do produce both males and females 

 at the end of the summer, the question is where have the male eggs 

 come from?* Beard appears to take for granted that a female egg 

 can give rise to cells that become male eggs. If so his theory can 

 have very little if any value, since the entire conception on which it 

 rests, namely, the separation of the male and the female eggs at one 

 division, is rendered valueless, I think, by the assumption that after 

 such a thing has once taken place a female cell may in the next 

 generation give rise to male eggs. Furthermore Beard's assumption, 

 that the separation of the male and the female eggs occurs at the time 

 when the reduction in the number of the chromosomes takes place in 

 the egg, is pure guess-work, and not very good guessing either, for 

 certain recent work indicates that the reduction in the number of the 

 chromosomes involves a process that can have no conceivable connec- 

 tion with the separation of the male from the female elements of the 

 egg. On the whole it does not appear that Beard has offered a very 

 convincing theory as to how the determination of the sex of the 

 individual is accomplished. 



Castlef also has recently advanced certain hypotheses in regard to 

 the determination of sex. In certain superficial respects his view 

 appears similar to that of Beard, but closer scrutiny shows that the 

 two views are essentially different in many important points. 



Castle assumes that there are two kinds of eggs, male and female, 

 and two kinds of spermatozoa, male and female. He supposes that 

 both kinds of spermatozoa are functional in the sense that each carries 

 with it the possibility of determining the sex of the individual, and 

 each spermatozoon is also capable of fertilizing an egg, but a male 

 spermatozoon can fertilize only a female egg and a female spermatozoon 

 a male egg. It is evident, therefore, that Castle's idea in regard to 

 the spermatozoa is fundamentally different from that of Beard. 

 Furthermore, Castle supposes that the separation of the male from 

 the female qualities of each egg takes place at the time when the 

 second polar body is extruded, and, in consequence, the egg and one 

 of the polar bodies will be female and the other two polar bodies male, 

 or if the egg remains female, one polar body will be female and the 



* The same paradox appears wherever a female contains male eggs. 



t Bulletin Museum Compt. Zoology at Harvard College, January, 1903. 



