730 GENERATION AND DEVELOPMENT. 



other times the serum is removed, andjthe fibrin consti- 

 tutes a solid stelliform mass. 



The yellow substance of which the corpus luteum con- 

 sists, both in the human subject and in the domestic 

 animals, is a growth from the inner surface of the Graafian 

 vesicle, the result of an increased development of the cells 

 forming the membrana granulosa, which naturally lines 

 the internal tunic of the vesicle. 



The first changes of the internal coat of the Graafian 

 vesicle in the process of formation of a corpus luteum, seem 

 to occur in every case in which an ovum escapes ; as well 

 in the human subject as in the domestic quadrupeds. If 

 the ovum is impregnated, the growth of the yellow sub- 

 stance goes on during nearly the whole period of gestation, 

 and forms the large corpus luteum commonly described as 

 a characteristic mark of impregnation. If the ovum is 

 not impregnated, the growth of yellow substance on the 

 internal surface of the vesicle proceeds, in the human ovary, 

 no further than the formation of a thin layer, which shortly 

 disappears ; but in the domestic animals it continues for 

 some time after the ovumlias perished, and forms a corpus 

 luteum of considerable size. The fact, that a structure, in 

 its essential characters similar to, though smaller than, a 

 corpus luteum observed during pregnancy, is formed in the 

 human subject, independent of impregnation or of sexual 

 union, coupled with the varieties in size of corpora lutea 

 formed during pregnancy, necessarily renders unsafe all 

 evidence of previous impregnation founded on the existence 

 of a corpus luteum in the ovary. 



The following table by Dalton, expresses well the dif- 

 ferences between the corpus luteum of the pregnant and 

 unimpregnated condition respectively. 



