THE MAMMALIAN SEXUAL CYCLE 51 



having a prolonged heat period. In the cat also o\^ilation does 

 not occur spontaneously. 



If a doe rabbit is allowed to copulate with a buck previously 

 made sterile (as by cutting the vasa deferentia but without 

 interfering with the testes) ovulation still takes places, but with- 

 out pregnancy supervening. Corpora lutea, however, are formed 

 in the ovaries, and pseudo-pregnant conditions supervene in 

 the uterus and mammary glands, to be followed in course of time 

 by regression and milk secretion, in the same kind of way as 

 in the marsupial and in the bitch. Pseudo-pregnancy cannot 

 occur normally in the rabbit owing to the fact that corpora 

 lutea are usually only produced after a coition which results 

 in pregnancy. 



The Menstrual Cycle 



The menstrual cycle in the Primates (man and monkevs) is 

 believed to correspond to the short or " dioestrous "" cycle of 

 the polyoestrous lower mammals, but there is still some doubt 

 as to the precise correspondence of the successive stages. It is 

 evident that in the Primates there is no anoestrum or prolonged 

 period of rest, but in monkeys the matter is complicated by the 

 apparent fact that whereas these animals experience an unbroken 

 succession of sexual cycles, each lasting about a lunar month 

 (as in man), the periods of breeding are restricted to particular 

 seasons (Heape). 



The uterine cycle in both monkeys and man has been divided 

 by Milnes Marshall, Heape, and others into four chief stages as 

 follows : — ■ 



(1) The constructive stage. 



(2) The destructive stage. 



(3) The stage of repair. 



(4) The stage of quiescence. 



During the constructive stage the uterus undergoes gro^vth, 

 glandular development, and hypersemia, i.e. increase in the 

 blood vessels, both in size and number. The changes in a 

 general way are described as being very similar to those which 

 occiu" at the commencement of pregnancy. 



At the beginning of the destructive stage the congested 

 vessels in the uterine mucosa break down, and blood is freely 



