CHAPTER III 

 SEXUAL PERIODICITY IN THE FEMALE MAMMAL 



Sexual periodicity in the mammalian female may be said to 

 consist of three cycles. The first — the attainment of puberty, 

 sexual maturity, and the decline of sexual function at the 

 menopause — is passed through but once. The second — the 

 periodic occurrence of the breeding season — appears one or 

 more times each year (or in extreme cases every two years). 

 Finally, the third consists of the cyclic periods of oestrus, at 

 which the actual mating takes place, and of which one or more 

 occur during each breeding season. 



{a) PUBERTY AND THE MENOPAUSE 



The development of the ovary before puberty tends to be 

 sporadic, and may include one or more waves of growth followed 

 by retrogressive changes. In the mouse, for instance, the growth 

 of the follicles is quite advanced at three weeks old, but de- 

 generation subsequently sets in, accompanied by a decrease in 

 the size of the ovary (80). The growth of the accessory organs, 

 on the contrary, appears to be gradual and continuous from the 

 time when they are first differentiated. The first abrupt change 

 in the accessory organs occurs at the first oestrous period, the 

 definite sign of the onset of puberty. The attainment of puberty 

 may thus be said to consist of two phases: 



(a) The gradual pre-pubertal development of the accessory 



organs. 



(b) The abrupt appearance of the first oestrus and ovulation. 



The first cestrous period, however, is the same as any other, 

 except for minor changes such as the appearance of the vaginal 

 orifice for the first time in the mouse and rat; the stimulus 



