THE REPRODUCTIVE ORGANS. 



219 



losa, epithelial in nature, now enlarge and probably also proliferate 

 so that this layer of cells becomes greatly thickened. The cells of 

 the connective tissue upon which the tunica granulosa rests also pro- 

 liferate and columns of them penetrate among the epithelial cells, 

 which they very closely resemble, and later these ingrowths of con- 

 nective-tissue cells become vascularized with loops of capillary blood- 



Fig. 197. 



Lutein cells 



Connective- 

 tissue septa 



Blood-vessel 



Part of a corpus luteum of a bitch. (X 300.) 



vessels sprouting from the older vessels of the stroma. While this 

 growth of connective tissue is taking place, the epithelial cells 

 undergo retrograde changes which are characterized by the appear- 

 ance of fat droplets in the cytoplasm, giving the tissue a yellow 

 color when they are abundant. For this reason the cells are called 

 lutein cells. This process gradually leads to the ultimate destruction 

 of the epithelium, which is replaced by connective tissue. Fibres 



