CHANGES IN THE OVARY 153 



the yolk of the degenerating ovum, which becomes filled with them. 

 Afterwards they are said to migrate, leaving nothing but connective 

 tissue which fills in the cavity of the follicle. A similar process is 

 described as occurring in certain reptiles. Perez 1 also has recorded 

 the phagocytic absorption of ova by follicle-cells in the ovary of 

 the fasting newt. 



Schottlander 2 states that atresia can occur by fatty degeneration 

 as well as by chromatolysis. 



Flernming 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. Leo Loeb 3 

 also says that in the rabbit the theca interna cells may enlarge 

 during atresia, becoming epithelioid and gland-like and that they 

 remain in this condition for some time. 



Heape 4 states that in the rabbit two kinds of degeneration 

 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. 5 Thus Sandes 6 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 luteurn, 

 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 



1 Perez, " Sur la Resorption phagocytaire des Ovules, etc.," Proces- Verbaux 

 de la Soc. des Sciences de Bwdeaux, 1903. 



2 Schottlander, loc. cit. 



3 Loeb, "The Relation of the Ovary to the Uterus and Mammary Gland," 

 Trans. Amer. Gyn. Soc.^ 1917. 



4 Heape, loc. cit. 



5 Marshall, " The CEstrous Cycle, etc., in the Sheep," Phil. Trans., B., 

 vol. cxcvi., 1903. 



6 Sandes, loc. cit. 



