806 



DEVELOPMENT OF THE TJRO-GENITAL OEGANS. 



tne middle of tl\e third month only traces of them are visible in the 

 human embryo. 



First origin of the Wolffian bodies. — Difference of opinion has 

 for some time existed among embryologists as to the exact source of 



3 "-■ 



fig. 601. — Tkaxsverse Section THRotJcn the Abdominal Region of the Chick ok 

 THE Third Day (from Kolliker). 



The explanation of tlic letters is the same as that in the previous figure. 



the rudiments of the uro-genital system, but it now appears to be fully 

 ascertained by the concurrence of a variety of observers, more especially 

 of Waldeyer, Scheuk, and Balfour, that the Wolffian duct, which is the 

 iirst part formed, and the formative substance of the AVolffian tubes 



Fisr. 602. 



d<l' 



Fig. 602. — Transverse Section of the Embryo-Chick of the Third Day 

 (from Kolliker). 



mr, medullary canal and medulla of the spinal cord ; en, notochord ; mch, primordial 

 •vertebral mass ; 7n, muscle-plate ; dr and (//, groove of the primitive intestine as formed 

 by the hyijoblast and splanchnopleure ; cio, one of the two aoi-tte : mw, Wolffian body ; 

 unff, Wolffian duct ; re, vena cardinalis ; h, epiblast ; hp, somatopleure and its reflection 

 into the amnion ; ^^j the p] euro-peritoneal space. 



and glomeruli, proceed from the mesoblast, and as these form the founda- 

 tion of the principal urinary and genital organs, it follows that this 



