126 THE PHYSIOLOGY OF REPRODUCTION 



the membrana granulosa lining the follicle, and the discus 

 proligerus surrounding the ovum. • The innermost cells of the 

 discus rest upon a thick, transparent, radially striated membrane 

 with a granular outer border. This is the zona radiata or zona 

 pellucida. The striated appearance is due to the presence of 

 fine canals. Within the zona, and immediately enclosing the 

 ovum, another very thin membrane can sometimes be made out. 

 This is the vitelhhe membrane. The membrana granulosa and 

 discus proligerus are united by one or more strands of f olUcular 

 epithehal cells. A viscid fluid, containing protein matter, collects 



between them and becomes gradually 

 increased in quantity as the follicle 

 continues to grow.^ 



The hquof folHculi begins to form 

 in the developing rat's ovary at about 

 the ninth day of pregnancy.^ Miss 

 Lane-Claypon suggests that the kary- 

 olytic changes which occur in the 

 nuclei of the follicular epithelial cells 

 may have some connection with the 

 origin of the liquor. She states, how- 

 ever, that in the process of formation 

 of the liquor folhcuU in the aidult 

 ovary, the follicle ceUs appear simply 

 to disintegrate and dissolve without 

 showing the phenomena of karyolysis. On the other hand 

 Honore,' who has investigated the subject in the case of the 

 rabbit, concludes that the liquor folUcuK is secreted by the 

 foUicle ceUs, without their undergoing destruction (or that, if this 

 occur, it is immaterial to the process of liquor formation), in the 

 same way as the urine is secreted by the epithelium of the renal 



' Occasionally a Graafian follicle may contain more than one ovum, but 

 this is abnormal. Such follicles have been described as occurring in the 

 rabbit's ovary by Honore (" Recherches sur I'Ovarie du Lapin," Arch, de 

 Biol., vol. xvii. 1901), and in the dog's ovary by Smyth (" An Unusual Graafian 

 Follicle," JBiol. Bvil., vol. xiv., 1908). The latter writer states that one follicle 

 contained seven ova. He shows that the tendency to produce multiple ova may 

 be hereditary, and that it is apparently correlated with a high fertility. 



^ Laue-Claypon, loc. cit. 



' Honore, " Recherches sur I'Ovarie du Lapin," Arch, de JBiol., vol. xvi., 

 1900. 



Fie. 29. — Young oocyte or 

 egg surrounded by a 

 single layer of follicular 

 epithelial cells. (From 

 van der Stricht.) 



