THE REPRODUCTIVE SYSTEM. 651 



consequence of the contraction of the external tunic of the vesicle. After 

 the orifice of the vesicle has closed, the growth of the yellow substance 

 continues during the first half of pregnancy, till the cavity is reduced to 

 a comparatively small size, or is obliterated; in the latter case, merely a 

 white stelliform cicatrix remains in the centre of the corpus luteum. 



An effusion of blood gene rally takes place into the cavity of the Graaf- 

 ian vesicle at the time of its rupture, especially in the human subject, 

 but it has no share in forming the yellow body; it gradually loses its 

 coloring matter, and acquires the character of a mass of fibrin. The 

 serum of the blood sometimes remains included within a cavity in the 

 centre of the coagulum, and then the decolorized fibrin forms a mem- 

 braniform sac, lining the corpus luteum. At other times the serum is 

 removed, and the fibrin constitutes a solid stelliform mass. 



The yellow substance of which the corpus luteum consists, 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 develop- 

 ment 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 domes- 

 tic quadrupeds. If the ovum is impregnated, the growth of the yellow 

 substance continues 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 ovum has perished, and forms a corpus luteum of con- 

 siderable size. The fact that a structure, in its essential characters 

 similar to, though smaller than, a corpus luteum observed during preg- 

 nancy, 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 011 the existence of a corpus luteum in 

 the ovary. 



The following table by Dalton, expresses well the differences between 

 the corpus luteum of the pregnant and unimpregnated condition respec- 

 tively: 



