HORMONES AND REPRODUCTION 65 



comb and wattles, while a woman may grow a beard 

 and develop a deep voice. However, in many such cases 

 the hormone responsible is not testosterone, but the 

 male-like hormone of the adrenal cortex. This cortical 

 hormone also has a close chemical relationship with the 

 natural androgens and oestrogens. 



A third hormone secreted by the ovary is that formed 



CH. 



.^^^Nyx/ 



Fig. 10. — The structure of a molecule 

 of progesterone. 



in the corpus luteum. Again the situation is best under- 

 stood in the mammals, and indeed it is often held that 

 true corpora lutea are peculiar to these animals. The 

 corpora-lutea-like bodies in the ovaries of the egg-laying 

 vertebrates ar^ often described as functionless, though 

 this has recently been seriously challenged.** 



The substance produced by the mammalian corpus 

 luteum is called progesterone, and it has a molecular 

 structure similar to those of the androgens and oes- 

 trogens. Of course, its action does not begin until after 

 the bursting of the Graafian follicle, that is after the 

 ©estradiol has exerted its full effect. At this moment 

 progesterone takes over to maintain and increase the 



