Page:Popular Science Monthly Volume 64.djvu/113

Rh 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 connection 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.

Castle 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