78 



FOLLICULAR DERIVATIVES IN VERTEBRATES 



III 



like formations, derived from ovarian follicles. Before 

 examining the origin of these corpora lutea we shall first 

 describe briefly the histology of the ovary and the develop- 

 ment of the ova and the follicles. 



The ovary of the bitterling is a thin-walled, pocket- 

 shaped, hollow organ. Its surface area is increased by the 

 formation of small pocket-like concavities in the wall (Fig. 

 6i). The wall itself consists of three layers of cells: (i) 

 a firm connective tissue layer, containing blood- and lymph- 

 atic vessels, collagen fibres, oblong connective tissue cells 

 with numerous xanthophores and melanophores; (2) the pe- 

 ritoneum, a very thin epithelium upon this connective tissue 

 layer on the outside; (3) a nuclear epithelium covering the 

 connective tissue layer on the inside. The cavity of the ovary 

 is continuous with the oviduct, the epithelium of which con- 

 tains mucous- and ciliated cells. In this way the ovary, with 

 its numerous egg-pouches, hangs in a space closed off from 

 the abdominal cavity and continues caudally into the ovi- 

 positor. 



The function of the ovary of the bitterling is ( i ) gene- 

 rative, by the production of mature ova; (2) regulative, by 



Fig. 62. The follicle of a luteogenic ovum: — 



1. capillary, 4, basal membrane, 6. oolemma, 



2. theca externa, 5, granulosa, 7. egg-plasm, 



3. theca interna, 8. yolk. 



