OPERATION OF THE GENETIC SYSTEM 7 1 



The answer to this question Is approached through a 

 series of experiments, the results of which we may sum- 

 marize: 



(6) Experiment: Remove the germ gland (testis or 

 ovary) from the very young individual, before the later 

 sex differences are produced. 



The result is that the later sex differences do not appear. 

 Both sexes remain nearly or quite in the indifferent condi- 

 tion, so far as sex differences are concerned, though they 

 continue to grow and develop In other ways. 



(7) It follows that the later sex differences are produced 

 through the action of the germ glands (ovary or testis). 

 The body cells of the two sexes still retain the differences as 

 to the number of X-chromosomes present, but without the 

 germ glands this does not result in the production of the 

 later sex differences. 



How do testis and ovary act in producing the later sex 

 differences? This is tested by another experiment: 



(8) Experiment: Interchange the germ glands of the 

 two sexes. Remove the ovary from a young female, and re- 

 place it by transplanting to the female body a young testis 

 taken from a young male (figure 23, A). 



Similarly, remove the testis from a young male and re- 

 place it by an ovary taken from a young female (figure 23, 



B). 



These experiments are difficult, but have been success- 

 fully carried out In rats by a number of Investigators. 



Result: The female body (XX) containing a testis (XO) 

 develops the male secondary sex characters! The male body 

 (XO) containing an ovary (XX) develops the female 

 secondary sex characters (such a male develops a mammary 

 gland that may produce milk; it may suckle the young). 



(9) The results of the experiments show that it Is the 

 nature of the germ gland (whether of the XX or the XO 

 type) that determines (mainly or entirely) what later sex 



