TYPES OF CESTROUS CYCLE 67 



amenorrhoea, while irradiation during the second half 

 {i.e. after the formation of the corpus luteum) does not 

 interfere with the next menstruation. 



The essential feature of the interpretation of the 

 menstrual period as purely pseudo-pregnant degenera- 

 tion is that preliminary activity of the corpus luteum is 

 presupposed. This conflicts with the well-established 

 fact that some humans (123, 314, 360), and many 

 monkeys, have been known to menstruate without 

 previous ovulation. Unless in such conditions men- 

 struation is purely pathological (which its regularity 

 makes very doubtful), its occurrence in non-ovulating 

 animals is strong support of the second theory of 

 menstruation. 



{b) From his studies on monkeys, Heape was led to suppose 

 that menstruation was analogous with the prooestrous 

 haemorrhage which takes place in such animals as the 

 dog, as described by Marshall and Jolly, and to a lesser 

 extent in the cow and sheep. A similar view was 

 initially held by Marshall. In general, the period of 

 cEstrus in mammals is characterized by destruction of 

 the epithelium of the genital tract, such as the cornifi- 

 cation of the vaginal epithelium in the rat, mouse, and 

 guinea-pig. This merely represents the disintegration 

 of a short prooestrous growth, and its identification with 

 menstruation (as attempted by Stockard and Papani- 

 colaou for the guinea-pig) is diflicult. Such a point of 

 view is strengthened, however, by the occurrence of 

 menstruation without ovulation, and by Allen's (12) 

 induction of menstruation in Macacus (a) by destruc- 

 tion of ripe follicles and (b) by injection into the 

 ovariectomized animal of the cestrus-producing 

 hormone. 



The view that menstruation is prooestrous degenera- 

 tion is difficult to reconcile with the time relations of 

 the uterine and ovarian cvcles. It is generally agreed 

 that ovulation takes place about fourteen days after 

 the beginning of the previous menstruation. In the 

 lower mammals ovulation and oestrus are strictly 



