DTOESTROUS CYCLE IN THE GUINEA-PIG 263 



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

 mucosa begins, the corpora lutea are almost completely degen- 

 erated. 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 the recently ruptured follicles. 



It, therefore, might be imagined that the secretion from the 

 corpora lutea exerts a protective influence over the uterus and 

 vagina while the absence of this secretion permits the breaking 

 down and degeneration of the uterine epithelium typical of the 

 'heat period.' 



