REPRODUCTION AND DEVELOPMENT. 281 



face. Each Graafian vesicle has an exceedingly vascular wall, 

 embracing the proper ovisac, and when the vesicle bursts, its 

 vessels, being no longer supported, give way, and fill the 

 cavity with a clot. This clot and the sac around it undergo 

 various changes; the clot disappearing, while the sac becomes 

 yellow, and increases in thickness and size, particularly when 

 impregnation has taken place. The structure which is thus 

 formed is called a corpus luteum, and subsequently dis^ 

 appears, leaving nothing but a cicatrix. It does not seem to 

 fulfil any function, but rather to be a growth resulting from 

 the vascular excitement of the structures around. 



205. In the male, the germ-preparing glands, corresponding 

 to the ovaries in the female, are the testes. They differ, how- 



Fig. 144. DIAGRAM OF SEMINIFEROUS TUBULES AND DUCTS, a, a, 

 Tubuli seminif eri ; b, b, vasa recta ; c, rete testis ; d, vasa effer- 

 entia, from twelve to fifteen in number ; 6, coni vasculosi ; /, /, 

 epididymis ; g, vas aberrans ; h, vas deferens. 



ever, from the ovaries, in leaving, before birth, their original 

 situation within the body, and descending to a position 

 external to the abdominal cavity; as also in being developed 



