154 THE PHYSIOLOGY OF REPRODUCTION 



The corpus luteum of pregnancy is sometimes distinguished 

 from the structure formed when pregnancy does not supervene 

 after ovulation, the latter being called the false corpus luteum, 1 

 or corpus luteum of menstruation ; but it is obvious that the two 

 bodies are identical in the early stages, and otherwise essentially 

 similar. 2 Moreover, according to Ancel and Bouin, 3 in animals 

 like the rabbit, which do not ovulate spontaneously during 

 oestrus, these two kinds of corpora lutea are identical throughout. 

 In such animals interstitial cells are believed to replace func- 

 tionally the " periodic corpus luteum." 



The hypotheses which have been put forward regarding the 

 function of the corpus luteum, and the possible part which this 

 organ plays in the metabolism of pregnancy, will be discussed at 

 some length in a future chapter. (For chemistry of corpus luteum 

 see p. 263.) 



THE ATRETIC FOLLICLE 



It has been already mentioned that the rabbit, the ferret, and 

 certain other animals do not necessarily ovulate during oestrus 

 in the absence of the male. The follicles, instead of bursting, 

 undergo degeneration (atresia) with their contained ova. Heape 4 

 has shown that the congested vessels in the wall of the follicle 

 may rupture and pour blood into the cavity, where it forms a 

 clot surrounding the degenerating ovum. The brilliant, suffused 

 red appearance of many of the rabbit's follicles during the early 

 stages of degeneration is said to result from internal bleeding. 

 The first rush of blood into the cavity washes away the 

 epithelium from the wall of the follicle, at the same time dis- 

 integrating the theca interna. Bleeding, however, does not 

 necessarily occur at all. In section the cavity of the degenerate 

 follicle appears, during the early stages, to be bounded by the 

 theca externa, while the ovum may be seen as a shrunken 

 object no longer enclosed by a discus proligerus. 5 Heape 6 



1 Or corpus luteum spurium. 



* The retrogressive changes are similar in both kinds of corpora lutea. 



3 Ancel and Bouin, " Sur les Homologies et la Significance des Glandes 

 ;i Secretion interne de 1'Ovaire," C. R. de la Soc. de Bid., vol. Ixvi., 1909. 



4 Heape, "Ovulation, &c.," Proc. Roy. Soc., B., vol. Ixxvi., 1905. 



5 Marshall, "The (Estrous Cycle in the Common Ferret," Quar. Jour. 

 Micr. Science, vol. xlviii., 1904. ' Heape, loc. cit. 



