Sex as an Adaptation 429 



Both Flourens and Cuenot found this to be the case in the 

 few instances that they examined, but Cuenot has shown that 

 this does not always happen. Even when this occurs, it has 

 not been determined whether the result depends on something 

 in the egg itself, that causes a male egg to be set free first, or 

 on some external condition that determines that the first egg 

 shall become a male. It has been claimed that the age of 

 the spermatozoon might in this and in other cases determine 

 the result ; but Gerbe has shown that if the domestic hen is 

 isolated for fifteen days after union with the male, she will 

 continue to produce fertile eggs from which both sexes are 

 produced, without showing any relation between the time 

 the eggs are laid and the particular sex that develops. 



Cuenot does not discuss whether sex is determined by the 

 nucleus or by the protoplasm, but if, as he thinks probable, 

 the size of the egg is a determining factor, it would appear 

 that the protoplasm must be the chief agent. Even if this 

 were the case it would still be possible that the size of the 

 egg itself might be connected with some action on the part 

 of the nucleus. If, as seems probable, identical twins come 

 from halves of the same egg, then, since they are of the same 

 sex, the absolute amount of protoplasm cannot be a factor 

 in sex determination. 



As a basis for the discussion that follows, certain processes 

 that take place during the maturation divisions of the egg 

 and of the spermatozoon must be briefly noticed. After the 

 egg leaves the ovary it extrudes a minute body called the 

 first polar body (Fig. 6 B, C, D). This process of extrusion 

 is really a cell division accompanied by the regular mitotic 

 division of the nucleus ; but since one of the products of the 

 division, the polar body, is extremely small, the meaning of 

 the process was not at first understood. The half of the 

 nucleus, that remains in the egg, divides again, and one of its 

 halves is thrown out into a second polar body (Fig. 6 E, 

 F, G). Meanwhile, the first polar body has divided into two 



