150 THE PHYSIOLOGY OF REPRODUCTION 



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 disintegrating the theca interna. This rupture of the 

 vessels must be interpreted as of the nature of an attempted 

 ovulation, since it apparently only takes place with mature follicles 

 which would have discharged had coition occurred. In other follicles 

 bleeding does not necessarily take place at all. In section the cavity 

 of the degenerate follicle appears, during the early stages, to be 



-^--'' "- 



Fia. 44. Section through follicle in early stage of degeneration. (From 

 Sellheim.) The ovum and follicular epithelium are in process of atrophy. 



bounded by the theca externa, while the ovum may be seen as a 

 shrunken object no longer enclosed by a discus proligerus. 1 Heape 2 

 states that the contents of the follicle are gradually absorbed through 

 the agency of ingrowing parenchyma cells and leucocytes. The 

 cavity is eventually filled in by the ingrowth of normal ovarian tissue. 

 The following characteristics serve to distinguish the degenerate 

 or atretic follicle (sometimes called the corpus luteum atreticum) 

 from the true corpus luteum : (1) There is no indication of any 

 rupture to the exterior. (2) The ovum, being retained in the follicle, 

 loses its regularly circular shape, becomes shrivelled, and gradually 

 disappears altogether. (3) The follicular epithelium, instead of 



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

 Science, vol. xlviii., 1904. 



2 Heape, lov. cit. 



