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§ 2 HISTOGENESIS OF CORPORA LUTEA 8i 



These cells later become theca cells. In these cell-islands there 

 is active cell-division resulting in the production of oocytes 

 which develop into ova. Not until then do the three com- 

 ponents, i.e. the ovum, the granulosa and the theca, join 

 together to form a follicle. Some of the granulosa cells sur- 

 round the ovum, and upon this simple granulosa layer the 

 theca cells are laid down. Thus, the follicle has come into 

 existence. Figs. 63 c and d show two different stages in the 

 development of the follicle: the proliferation stage and the 

 completed follicle. 



Although the notion "follicle" is used in connexion with the mam- 

 malian ovary, and w'as originally conditional upon the presence of a 

 follicular cavity, we propose to retain it in the present context, although 

 no cavity is formed in the follicles of the fish. In the primary follicle of 

 mammals, however, there is no cavity, and one might say, therefore, 

 that the ovular follicle of the fish remains at the primary stage for the 

 duration of its life. 



The ovum and the follicular wall grow steadily until 

 maturity. Four different stages in the growth of the ovum 

 may be distinguished. 



a. Small ova; average diameter 100 ju (10 — 200 /i): 

 ovular cytoplasm, acidophil; no yolk present. 



b. Medium-sized ova; average diameter 300 jli (200 — 

 ^00 jLi); ovular cytoplasm; basophil; primary yolk formation 

 has started; no oolemma present. 



c. Large ova; diameter between 500 and 1000 jti; ovular 

 cytoplasm, basophil; secondary yolk and oolemma formation 

 begins. 



d. Maturing and mature ova; diameter between 1000 and 

 1800 /ii. The ovular cytoplasm is divided into a vegetative 

 part containing the yolk, and an animal part containing the 

 nucleus; a thick oolemma envelops the egg. 



§ 2. HISTOGENESIS OF THE CORPORA LUTEA 



We have already mentioned that, in our view, it seems as if 

 corpora lutea with a secretory function occur in the ovary of 

 fishes. This is surprising, since up to the present no such 

 appearance of corpora lutea in anamnia has been observed. 



