62 



VERTEBRATE REPRODUCTIVE CYCLES 



that this process is stimulated by I.C.S.H. Once formed, 

 the corpus luteum is itself an endocrine gland. In the 

 mammals the hormone that it secretes is known as 

 progesterone, the functions of which are described on 

 p. 65. In the lower vertebrates the only information 

 available is that concerning the bitterling in which it 

 has been suggested that the corpus luteum produces a 

 hormone called oviductin.** This is discussed on p. 66. 



7. THE OVARIAN HORMONES 



The most important hormones produced by the 

 vertebrate ovary are those known as the female or 

 oestrogenic hormones. It is thought that the substance 



HO 



^^\y\y 



Fig. 9. — The structure of molecule of 

 oestradiol. 



actually secreted by the mammalian ovaiy is oestradiol, 

 and this is the most active natural oestrogen known. 

 Other oestrogens occurring naturally in the body are 

 oestrone and oestriol, which are perhaps formed from 

 oestradiol by oxidation. A variety of other chemically 

 related substances have been synthesized, and many of 

 these induce similar physiological effects. However, 

 oestrogenic activity does not seem to be the property of 



