112 THE PHYSIOLOGY OF REPRODUCTION 



the germinal epithelium. The tubular ingrowths had already been 

 noticed by Valentin/ who, however, failed to recognise their connection 

 with the germinal epithelium. Later observers, however, did not 

 confirm the tubular origin of the ovary. 



To Waldeyer belongs the credit of first recognising the true 

 nature and significance of the process of egg formation, an account of 

 which was published in his famous monograph, Eierstock und Ei? 

 He found that in the chick, on the fourth day of development, the 

 ccelomic epithelium which covers the inner surface of the Wolffian 

 body became differentiated from the tissue surrounding it, the cells 

 being relatively large and cuboidal in shape. A little later he 

 observed that the cells had multiplied to such an extent as' to give 

 rise to a distinct elevation. In this way the germinal epithelium 

 was formed, and this marked the site of the future ovary. The 



Fig. 26. — Section. through ovary of pig embryo. (From Williams' 

 Obstetrics, Appleton & Co.) 



G.E., Germinal epithelium ; S., stroma. 



fnesoblast underlying the germinal epithelium is described as growing 

 upwards among the cells of the latter, and so giving rise to the 

 appearance of those germinal ingrowths or " egg-tubes," which were 

 described by Pfl tiger. 



The cells of the germinal epithelium are thus divided by mesoblast 

 into clusters of "egg-nests" which contain the primordial ova, as 

 Waldeyer has shown. As a result of this process two zones of tissue 

 are formed in the future ovary. The outer or cortical zone consists 

 of clusters of cells derived from the germinal epithelium, with 

 mesoblastic processes in between them. The inner or medullary 

 zone is composed at first entirely of mesoblast, which gives rise to 

 the vascular tissue and stroma of the ovary. 



The majority of investigators, including Balfour,^ Schafer,* Nagel,^ 



1 Valentin, "Ueber die Entwickelung der Follikel in dem Eierstocke der 

 Saugethiere," Miiller's Arch., 1838. 



^ Waldeyer, Eierstock und Ei, Leipzig, 1870. 



^ Balfour, "Structure and Development of the Vertebrate Ovaiy," Quar. 

 Jour. Micr. Science, vol. xviii., 1878. 



* Schafer, " On the Stiucture of the Immature Ovarian Ovum, etc.," Proc. 

 Roy. Soc; vol. XXX., 1880. 



5 Nagel, "Das menschliche Ei," Arch. f. MiJcr. Anat., vol. xxxi., 1888. 



