THE PRONEPHROS 



I 97 



A Pronephric duct 



^jj~ Mesodermal 

 segments 



Neural lube- 



Pronephric tubu 



Anlages of Pronephric 

 duct 



Nephrotome 

 Somatic mesoderm 



Splanchnic mesoderm 



Coelom Notochord Entoderm 



FIG. 204. Diagrams showing the development of the pronephric duct and pronephric tubules 

 (modified from Felix). A represents a later stage than B. 



Neural ti, 



'Mesodermal segment 



%^ASSy 

 -fa *%$ y j 



Notochord Q vgfy 



Cavity of git 

 Splanchnic mesoderm- 



Mesoderm of yolk sac. 



Intermediate cell mass 



Anlage of extremity 



'Codom 



8 /'I 



u' ffi'^ff Somatic mesoderm 



Umbilical vein 



FIG. 205. Transverse section of a 2.4 mm. human embryo, showing the intermediate cell mass 



or nephrotome (Kollmann). 



