404 Experimental Zoology 



male can be identified by its size, two such chromosomes have 

 been shown by Wilson to exist in the egg. 



In these cases we have conclusive evidence that sex is asso- 

 ciated with certain kinds of spermatozoa. Two important 

 considerations arise : first, in what way does this take place ; 

 and second, can we extend the same conclusion to other forms ? 

 Let us examine in turn these two questions. 



How does the spermatozoon with the accessory produce the 

 female? Two possibilities immediately suggest themselves, 

 either the accessory chromosome contains the elementary char- 

 acters of the female sex, or it produces its results quantitatively. 

 The former alternative rests on the assumption that the chro- 

 mosomes contain the unit-characters of the germ-cells. It is 

 this view of the chromosomes that in general meets with wide 

 favor at the present time. Historically it goes back to the 

 gemmule hypothesis of Darwin, the pangenes of de Vries, the 

 biophors of Weismann, etc. not to give other examples. 

 Those who believe that the characters of the species are con- 

 tained in living units of the germ that reside in the chromosomes, 

 and wander outward into the cell to bring about the cytoplas- 

 mic differentiation, will probably accept this first alternative in 

 regard to the influence of the accessory ; but those who find this 

 view improbable will be more inclined to the alternative view. 



There is one objection to the idea that the accessory carries 

 the female pangenes, that Wilson has pointed out, and which 

 may be a serious difficulty for this view. If we follow the history 

 of the accessory, we find that it passes from the female-producing 

 sperm into the egg to form there one of the pair of chromosomes 

 homologous with the accessory. In the next generation the 

 homologous chromosomes in the egg are supposed to separate 

 again, one going into the polar body and one remaining in the 

 egg. Now on the theory of chance, either one of the pair might 

 remain in the egg, and should it happen to be the " male-deter- 

 mining" chromosome, the egg should give rise to a male if en- 

 tered by a male-determining sperm ; but if entered by a female- 

 determining sperm (i.e. with the accessory), the two chromosomes 



