lOO THE DETERMINATION OF SEX 



tion, but on the contrary agrees with it fully. Morgan dis- 

 covered that when the sexual cells in the male develop in order 

 to produce spermatozoa, they form at their second division 

 two elements of unequal size. Fig. 53 reproduces two series 

 or Morgan's original pictures. In the first series, a-c, and 

 also in the second, d-f, the peculiar division is represented. 

 The big accessory chromosome moves into the larger of the 

 two elements, whech then develops further and becomes a 

 spermatozoon. The small element, meanwhile, shrivels up. 

 Thus there arise in these animals only spermatozoa with the 

 extra chromosome, and accordingly the fertilized ova become 

 females. 



American investigations, both those mentioned and others 

 related to them, lead us to the conclusion that sex is determined 

 by peculiarities of the cells, and not by external conditions. 

 If an external factor influences the proportion of the sexes, 

 this must happen, according to our new interpretation, by 

 interfering with the development of one or the other sex. In 

 the case of hermaphrodites, interference may act by favoring 

 the transformation of indifferent germ cells in one direction or 

 another. 



That the determination of sex dwells in the cells is made 

 probable also by the phenomenon of polyembryony. We 

 have already learned that four embryos arise from a single 

 Armadillo egg. They are always of the same sex. So also 

 in the case of small insects, the parasitic Chalcidse. Accord- 

 ing to the investigations of Bugnion, Marshall and Silvester, 

 many embryos arise from each single egg, and they are all of 

 the same sex. We can explain this wonderful phenomenon 

 only by the assumption that the sex of the egg is determined 

 from the start. 



It must be mentioned that, according to the investigations 



