VII.] THE SEX-UAL EMINENCE. 221 



The median portion of the ridge is occupied by the 

 projection of the Wolffian body, and here the epithelium 

 rapidly becomes flattened. 



On the inside of the ridge however, that is on the side 

 looking towards the splanchnopleure, the epithelium not 

 only retains its columnar character, but grows several 

 cells deep (Fig. 71, a), while at the same time the meso- 

 blast (E) underlying it becomes thickened. In this 

 way, owing partly to the increasing thickness of the 

 epithelium, and partly to the accumulation of mesoblast 

 beneath it, a slight eminence is formed, which when 

 viewed from below, after opening the abdominal cavity, 

 appears in direct light as a fusiform white patch or 

 streak, in its early stages extending along the whole 

 length of the Wolffian body and genital ridge, but sub- 

 sequently restricted to its anterior portion. Its appear- 

 ance under these circumstances has been well described 

 by Von Baer. 



This 'sexual eminence' is present in the early stages 

 of both sexes. In both the epithelium consists of several 

 layers of short cylindrical cells, a few of which are con- 

 spicuous on account of their size and their possessing a 

 highly refractive oval nucleus of considerable bulk; in 

 both, the underlying thickened mesoblast consists as 

 indeed at this epoch it does generally in all parts of the 

 body of spindle-shaped cells. 



The larger conspicuous cells of the epithelium 

 which appear to have quite a common origin with their 

 fellow cells and to arise from them by direct differen- 

 tiation, and which are seen at the first in male as 

 well as female embryos, are the primordial ova or pri- 

 mitive germinal cells (Fig. 71, o). Thus in quite early 



