HERMAPHRODITISM 167 



the relation of the secondary sexual characters to the 

 sex glands. In insects the characters in question are not 

 dependent on the presence or absence of these glands. 

 Hence, when such conditions occur after fertilization, 

 as those I have just considered, each part may develop 

 independently of the rest. 



HERMAPHRODITISM 



In almost all of the great groups of animals a condi- 

 tion is found in which complete sets of ovaries and testes 

 occur in the same individual. This condition is called 

 "hermaphroditism." In some groups of animals, as in 

 flatworms, leeches, mollusks, hermaphroditism is the 

 rule, and it is the common condition in flowering 

 plants. Sometimes there is only one system of outlets 

 for eggs and sperm, but not infrequently each has a 

 separate system. 



Here there is no problem of the production of males 

 and females, for one kind of individual alone exists. 

 But what determines that in one part of the body 

 male organs develop, and in another part a female 

 system ? 



^Two views suggest themselves, either somatic segre- 

 gation, or regional differentiation. By somatic seg- 

 regation I mean that at some time in the development 

 of the embryo — at some critical division — a separa- 

 tion of chromosomes takes place so that an egg-produc- 

 ing group and a sperm-producing group is formed. 

 There is no direct evidence in support of this view. 



Another view is that the formation of ovary and 

 testis is brought about in the same way as all 

 differentiations of body organs, as for example the 



