MOKPHOLOGY OF THE HUMAN URINOGENITAL TRACT. 355 



A very important point has now to be considered — viz., that 

 in connection with the mesonephros a sexual gland develops, 

 the future testis or ovary, as the case may be. 



The indifferent sexual gland first arises in the human foetus 

 about the end of the first month (fig. 34). Nagel has figured it 

 in foetuses of 12 mm., and Coste has an excellent drawing of it 

 at the same period. It is due to a tliickening of the coelomic 

 epithelium over the mesonephros, and by the ingrowth of this 

 epithelium the ova or seminiferous tubules, as the case may be, 

 arise. In the male, tubules connect the "Wolffian duct with the 

 seminiferous tubules, and in this way the Wolffian duct becomes 

 the seminal duct (epididymis and vas deferens). This phase of 

 development in the male need not further concern us, especially 

 as many of the points in regard to the development of the testis 

 require elucidation. As to the development of the ova and 

 Graafian follicles, a good deal of dispute exists ; but the most 

 generally accepted view is that the ova are derived from an 

 indipping of the cells of the germ epithelium into the connec- 

 tive tissue of the ovary, and that the cells of the membrana 

 granulosa have also a similar origin. Foulis, on the other hand, 

 believes in an outgrowth of the stroma snaring in the germ- 

 epithelium cells, and that the membrana granulosa cells arise 

 from the connective tissue. My specimen of a month old shews 

 the sexual gland present, and ova in course of formation. 



B. — The significance of the temiMrary develojniient of the 

 WoJfiian bodies in the human Embryo. 



As is well known, the mesonephros has only a temporary de- 

 velopment in the Amniota, but persists as a permanent kidney 

 (kidney and testis in the male) in tlie Anamnia. Thus, in the 

 human foetus the mesonephros reaches its full development 

 during the second month and then withers, leaving traces only, 

 although the duct has a more permanent adult function. The 

 question arises, therefore. Why do we get this temporary 

 development in the human foetus ? Why does the true kidney 

 not develop earlier ? 



The usual view is based on the Darwinian theory, and would 

 regard the mesonephros as an ancestral inheritance, used, so far 



