88 THE DETERMINATION OF SEX 



from the rest. It appears when a sexual cell begins its trans- 

 formation. At this time the chromosomes arise in the reduced 

 number and it is easy then to distinguish the one chromosome 

 which McClung has named the accessory. When the sexual 

 cell has formed the reduced number of chromosomes it is called 

 a spermatocyte. The spermatocyte divides, and at the same 

 time all the chromosomes, including the accessory, also divide. 

 The two daughter cells quickly divide again and so also do 

 the ordinary chromosomes, but this time the accessory chromo- 

 some does not divide, but passes undivided into one of the daughter 

 cells of the second generation. In this way four cells arise as 

 always in spermatogenesis, and of these four ceUs two have 

 each an accessory chromosome and two have none such. The 

 four cells pass through further changes in order to become 

 mature spermatozoa. Thus it comes about that we have in 

 these insects two kinds of spermatozoa, for half of them con- 

 tain a piece of the accessory chromosome and the other half 

 do not. From these facts McClung drew the conclusion that 

 the two kinds of spermatozoa determine the sex, and since he 

 found the accessory chromosomes in the cells of the male body, 

 he further supposed that the accessory chromosomes have to 

 do with the creation of the male sex. The observations of 

 the Kansas zoologists have been repeatedly confirmed by 

 other Americans. They are so easily made and are so signifi- 

 cant that we have demanded for several years past that our 

 medical students at Harvard should study the spermatogenesis 

 of grasshoppers. That the accessory chromosome stands in 

 immediate relation to the production of sex must be considered 

 as estabUshed, but I must immediately caU your attention to 

 the fact that McClung's theory acquired an essential further 

 development through E. B. Wilson,** who, in the investigation 

 of the relations of chromosomes in female insects, was able 



