DIOESTROUS CYCLE IN THE GUINEA-PIG 251 



tissue of the theca foUiculi into the hypertrophied foUicular epi- 

 thehum (fig. 26). This condition is more advanced during the 

 fourth stage, when reparation begins in the uterus. Figures 27 

 and 28 illustrate two corpora lutea from the same ovary during 

 the stage of uterine hemorrhage, the two are cut in different 

 directions. The ingrowth of the vascular tissue toward the cen- 

 tral cavity is apparent in these two figures. A well formed 

 mature corpus luteum is shown in figure 29, taken from a sec- 

 tion through the ovary of an animal about four and a half days 

 after the heat period when the uterus was in a typical resting 

 condition (fig. 10). 



8. GENERAL CONSIDERATIONS 



After a review of the above described facts there are several 

 problems of general importance which may be profitably dis- 

 cussed in connection with them. 



A fact of considerable significance is that the development 

 and the degeneration of the uterine and vaginal mucosa corre- 

 sponds very closely to the development and degeneration of the 

 corpora lutea in the ovaries. At the time when the corpora lutea 

 are highly developed and apparently active the mucosae of the 

 uterus and vagina show a normally vigorous and healthy con- 

 dition (cf . figs. 10 and 29) . While on the other hand when the 

 corpora lutea begin to degenerate during the second week after 

 the 'heat period' the mucosae of the uterus and vagina also 

 begin to show" signs of degeneration and the process of desqua- 

 mation slowly commences. At about two weeks after the last 

 'heat period,' when the wholesale destruction of the mucosa 

 begins, the corpora lutea are almost completely degenerated. 



The breaking of the Graafian follicles occurs during the oestrus 

 as a result of a congestion which began in the theca folliculi at 

 about the same time as the congestion of the stroma of the uterus 

 and vagina. And finally when the regenerative growth of the 

 uterine mucosa sets in, the ovaries then possess new corpora lutea 

 in an active state of differentiation which were derived from 

 these recently ruptured follicles. 



