02 FOLLICULAR DERIVATIVES IN VERTEBRATES 

 Atresia 



III 



Fig. 72. Modifications of the atretic type. 



a. The modifications of the atretic type (Fig. 72). 



a. The folliculus atreticus cavus is characterized by dege- 

 neration of the ovum and of the granulosa, followed by only 

 slight hyperplasia and hypertrophy of the theca, as a result 

 of which a cavity remains. Several old follicles may, either 

 in the normal course or after administration of certain gona- 

 dotrophic hormones, change into such atretic follicles (Fig. 

 72a). 



/5. The corpus atreticum solidum has the same preliminary 

 phases; but in contradistinction to the atretic follicle there 

 occurs marked hyperplasia and hypertrophy, owing to which 

 the entire ovular and granulosa space not only becomes filled 

 with theca-lutein tissue, but which also causes the whole 

 gland to increase considerably in size (Fig. 72b). 



y. The corpus atreticum mixtum shows only oolysis, and 

 no degeneration of the granulosa, so that a mixture of these 

 two follicular tissues is created. Although the persisting gran- 

 ulosa forms lutein cells, it remains small in amount, where- 

 as the theca is hypertrophied and forms a large thecal gland. 



