Basis of Sex Determination 209 



egg the second X chromosome. But if the male bee pro- 

 duces two types of spermatozoa we should expect that 

 only one-half of the fertilized eggs should be females, 

 the other half males. But it happens that of the two 

 types of spermatozoa only one is formed since in one of 

 the cell divisions which lead to the formation of sperma- 

 tozoa one viable spermatozoon only is formed while 

 the other one perishes. It is, therefore, quite pos- 

 sible that it is the female-producing spermatozoon 

 which survives while the male-producing spermatozoon 

 dies. 



It is occasionally observed that an insect shows one 

 sex on one side of its body and the opposite sex on the 

 other side. Boveri suggested that this phenomenon of 

 gynandromorphism is due to the fact that the spermato- 

 zoon for some unknown reason does not fuse with the 

 egg nucleus until after the egg has undergone its first 

 cell division. In this case it fuses with the nucleus of one 

 of the two cells into which the egg divides (or in some 

 cases even one of the later cells?). As a consequence 

 the one-half of the embryo which arises from the cell 

 which was not fertilized would have only one X chromo- 

 some and in a case like the bee would develop par- 

 thenogenetically, while the other half of the body, 

 developing from the cell into which a spermatozoon 

 has penetrated, would be fertilized. The latter half 

 of the body would be female, the former male. In his 

 last paper before his untimely death, Boveri has given 

 14 



