158 THE PHYSIOLOGY OF REPRODUCTION 



similar process is described as occurring in certain reptiles. 

 Perez l also has recorded the phagocytic absorption of ova by 

 follicle cells in the ovary of the fasting newt. 



Schottlander states that atresia can occur by fatty degenera- 

 tion as well as by chromatolysis. 



Flemming and others have described nuclear spindles in the 

 ova of follicles in an early stage of atresia, thus showing that 

 these had reached maturity before degeneration set in. 



Atretic follicles may shrivel up rapidly, or continue for a time 

 in a cystic condition. In the latter case the cavity remains 

 filled with fluid. Kolliker has shown that certain of the cells 

 in the theca interna of cystic follicles may undergo a process of 

 hypertrophy ; and the same fact has been noticed by Seitz, who 

 calls these cells " theca lutein cells" owing to their resemblance 

 to the cells of the corpus luteum. Seitz found these cells only 

 during pregnancy. 



Heape 2 has shown that in the rabbit two kinds of degenera- 

 tion prevail. In the one kind the changes first affect the follicle 

 and then the ovum, as described above. In the other the ovum 

 is first affected and the follicle afterwards. Heape interprets 

 the latter change as evidence that the ovum is not capable of 

 assimilating the nourishment supplied to it. 



Atresia is commonly stated to occur most frequently during 

 pregnancy, but it may occur at other times. 3 Thus Sandes 4 has 

 shown that in Dasyurus, as soon as the corpus luteum is formed, 

 the surrounding follicles which were previously in various stages 

 of active development begin to undergo atrophy. The process 

 begins in the follicles in closest proximity to the newly formed 

 corpus luteum, and is continued during pregnancy in the other 

 follicles in ever-widening circles. Sandes suggests that this 

 occurs as a result of mechanical pressure due to the growth of 

 the corpus luteum, or is in some way effected by the internal 

 secretion which the latter organ is supposed to elaborate. 

 Heape 5 states that in the case of the rabbit, if the buck is with- 



1 Perez, " Sur la Resorption phagocytaire des Ovules," &c., Procis- 

 Vtrbaux de la Soc. des Sciences de Bordeaux, 1903. 



2 Heape, loc. cit. 



3 Marshall, "The (Estrous Cycle. &c., in the Sheep," Phil. Trans., B., 

 vol. cxcvi., 1903. 



4 Sandes, loc. cit. s Heape, loc. cit. 



