Development of the Fourth Day 239 



in depth. At the same time the mesoblast of 

 that region becomes thickened to form a dense 

 area under the epithelial cells (Fig 74, EE). 

 This is the true genital ridge or sexual emi- 

 nence, from which the ovary or testis will be 

 formed. 



Certain of the cells of the germinal epithe- 



FIG. 74. TRANSVERSE SECTION THROUGH THE 

 WOLFFIAN BODY. (After Duval.) 



Aff, aorta. CSW, segmental tube. EE^ germinal epi- 

 thelium. 67, glomeruli. M, Miillerian duct. WC^ Wolffian 

 duct. 



(The position of the Miillerian duct (M) is apparently 

 wrongly indicated in this figure. It should be on the outer 

 side of the Wolffian duct.) 



Hum soon become distinguishable from the 

 rest, on account of their greater size, more 

 rounded outline, and large nuclei. These con- 

 spicuous cells, which have a common origin 

 with the other epithelial cells of the genital 

 ridge, are the primitive germ cells or gonoblasts 



(Fig. 74)- 



Up to this stage the development is the 



