20 INTERNAL SECRETIONS OF THE OVARY 



causing the first oestrous period must be supposed to be the same 

 as that responsible for the later ones. The problem of the 

 causation of puberty thus resolves itself into two parts: 



(a) What stimuli cause the gradual pre-pubertal development 



of the accessory organs? 



(b) By what means is the oestrus-producing stimulus first set 



in motion? 



These questions are discussed later (see p. 123). 



Functional puberty is attained in many animals (notably in 

 man) before body growth is completed. This is an anomaly, 

 since animals becoming pregnant before growth is completed 

 rarely reach maximum size. In the rat, according to Long and 

 Evans (425), the vaginal orifice usually appears a little before the 

 first ovulation. In the mouse and the rat it has been observed 

 that the intervals between the first few oestrous periods tend to 

 be somewhat longer than normal (425, 491). 



Long and Evans give the following data for the attainment of 

 puberty in the rat: 



Table i. — Attainment of Puberty in the Rat 

 (after Long and Evans). 



Age at opening of vagina 

 Age at first ovulation - 

 Length of ist cycle 

 Length of 2nd cycle 

 Length of 3rd cycle 

 Length of 4th cycle 



Average. 



72nd day of life 

 77th day of life 

 10 days 



9 days 



8-5 days 



7-5 days 



On the whole, however, the remarkable thing about the onset of 

 puberty is that the normal periodic activity is attained so 

 abruptly. 



The decline of sexual function at the menopause is character- 

 ized by retrogressive changes in the ovaries and by the gradual 

 atrophy of the entire accessory sexual apparatus — Fallopian 

 tubes, uterus, vagina, vulva, and mammary glands. These 

 changes, which finally are similar to those occurring after 



