THE DETERMINATION OF SEX 83 



difference, the essence of which consists in the production of 

 eggs or spermatozoa. 



By no means seldom do we find animals or plants which 

 are hermaphroditic organisms and produce both sexual 

 elements. Biologists very commonly hold the opinion that 

 hermaphroditism represents the primitive relation. Analysis 

 of the relations, however, seems to me not to lead to this 

 conclusion, and I propounded in 1892 the hypothesis 39 that 

 originally every animal individual is sexually indifferent. 

 Expressed in this form the hypothesis is not exact. It may 

 be more correctly expressed thus: This sexually indifferent 

 condition is primitive. We learned in the third lecture the 

 history of the sexual cells. These cells, however, are not sex- 

 ual elements, but every one of them must pass through a 

 very complicated and remarkable transformation in order to 

 become a sexual element. This fact in my opinion renders it 

 certain that the primitive condition was an indifferent one. 

 After it ensue the alterations which transform a sexless into 

 a sexual individual. 



When a cell divides the nucleus usually passes through a 

 so-called mitotic change which leads to the division of the nu- 

 cleus. During this change chromosomes appear. Each chro- 

 mosome is a separate granule which is formed by the concen- 

 tration of a small part of the nucleus, Fig. n. After the divi- 

 sion is completed the chromosomes become indistinct and are 

 at the same time utilized for the restoration of the normal 

 structure of the resting nucleus. Hence the chromosomes are 

 visible only during the process of division. It has been ascer- 

 tained that the number of chromosomes in each species is con- 

 stant,* although in different species their number may vary 



* This statement is not exact, for in certain cases, ascaris, etc., the number 

 of chromosomes varies with the period of life, and it is probable that in somatic cells 



