REPRODUCTIVE ORGANS IN ANIMALS 27 



of a bunch of small grapes, each grape representing a follicle. 

 The ovaries also contain degenerate or atrophic follicles, and it is 

 interesting to note that degeneration may set in at all stages 

 of groAAi:h, so that atrophic follicles are of varying sizes. In such 

 follicles the entire contents degenerate, and the cavity becomes 

 eventually filled in by new ingrowi^h of connective tissue. Some 

 of these follicles contain blood clots resulting from the rupture 



Fig. 15, — Section through ovary of rabbit, showing follicles and ova 

 in different stages of development. (L. F. Messel.) 



of the vessels in the connective tissue wall, and when this occurs 

 (as in the rabbit) the ovum and follicular epithelium are swept 

 to one side by the inrush of blood. The ovaries may also contain 

 yellow^ pigmented bodies known as corpora lutea. The corpus 

 luteum is formed from the ruptured follicle after the ovum has 

 been discharged (at ovulation), the epithelial cells undergoing 

 a great hypertrophy and becoming surrounded by a network 

 of connective tissue which with its contained blood vessels grows 

 inwards from the wall. Lipoid substances are subsequently 



