380 EMBRYOLOGY. 



(2) lying on its inner surface, an epithelium composed of many layers 

 of small follicular cells (fz), the membrana granulosa ; (3) the liquor 

 folliculi (ff) ; and (4) the ovum (ei), which originally lay in the centre 

 of the follicle, but which has now been crowded to the periphery. 

 Here, enveloped in a great mass of follicular cells (fz 1 ), it causes an 

 elevation of the wall, the discus proligei'us, which protrudes into 

 the cavity. 



When the egg has reached complete maturity its elimination 

 occurs by a collapse of the Graafian follicle, which has then at- 

 tained in Man a diameter of about 5 mm. and causes an elevation 

 at the surface of the ovary. The liquid of the follicle flows out 

 through the rupture and at the same time carries away with it 

 from the discus proligerus the egg, which comes first into' the body- 

 cavity, being surrounded by a small number of follicular cells, which 

 still cling to the zona pellucida (fig. 5). The egg is then taken up 

 by the oviduct. 



Into the cavity of the follicle produced by the flowing out of the 

 liquid an effusion of blood takes place from the ruptured blood-vessels 

 in the vicinity. The blood coagulates, and, accompanied by a prolif era- 

 tion of the adjacent tissue, is converted into the yellow body, or corpus 

 luteum, which is a characteristic structure of the ovary of Vertebrates. 

 Both the follicular cells (membrana granulosa) which are left behind 

 and the connective -tissue follicular capsule participate in this pro 

 liferation. The follicular cells continue to multiply, penetrate into 

 the interior of the coagulum, and after a time begin to undergo 

 degeneration and to be dissolved into a granular mass. Vascular 

 outgrowths from the capsule penetrate into the yellow body, and 

 at the same time there is an extensive emigration of white blood- 

 corpuscles or leucocytes, which likewise undergo fatty and granular 

 degeneration at a later period. 



It is of great importance for the further development of the yellow 

 body whether the egg set free is fertilised or remains unfertilised. 

 For according as the one or the other event supervenes, the corpus 

 luteum is distinguished as true or false. In the first case it acquires 

 a much greater size, the maximum of which is reached in the fourth 

 month of pregnancy. It then appears as a fleshy reddish mass. 

 After the fourth month a process of degeneration begins. The 

 products of degeneration, which have resulted from the granular 

 metamorphosis of the follicular cells and leucocytes, as well as from 

 the coagulum of blood, are absorbed by the blood-vessels. Out of the 

 decomposed coloring matter of the blood there have arisen haema- 



