REPRODUCTION 77 



It is the process of forming two or more 

 human embryos from the substance of one 

 egg that has given color to the statement that 

 man does exhibit at times non-sexual repro- 

 duction, for the differentiation of two or more 

 embryos from the mass of cells that would 

 ordinarily produce a single one is apparently 

 a process of budding, and in this respect it 

 may be maintained that man occasionally re- 

 produces non-sexually. 



But this aspect of identical twins, interest- 

 ing as it may be to the philosophical zoologist, 

 is of much less significance than that which 

 touches on the determination of sex. This oper- 

 ation is not only known through the condi- 

 tion in identical twins to be associated with a 

 very early stage of development, but evidence 

 from certain lower animals, chiefly the insects, 

 indicates that it is involved in the very earliest 

 stages of the differentiation of egg cells and 

 sperm cells. This is well illustrated in Pro- 

 tenor belfrageiy an insect closely related to the 

 squash bug. When the ordinary cells in the 

 body of the female of this insect divide, 

 the number of those peculiar nuclear bodies 

 known as chromosomes is seen to be fourteen. 

 In the formation of the egg cells, as might be 



