220 



THE MESODERMAL DERIVATIVES 



vein. The entire pronephric mass is surrounded by the connective 

 tissue of the pronephric capsule, derived from the adjacent somatic 

 mesoderm and myotome. 



Between each nephrotome and the dorsal aorta, suspended into the 

 body cavity and surrounded by splanchnic mesoderm, a very rudi- 

 mentary capillary network known as the glomus arises from the 

 dorsal aorta. This appears to be an abortive attempt to develop a 

 glomerulus characteristic of the adult mesonephric kidney, and occurs 

 in response to inductive influences from the non-functioning proneph- 

 ric tubules. 



The pronephros is structurally much like the functional kidney of 

 the frog, except that it is much less complex. It acquires a rich vas- 

 cular supply, both arterial and venous, but has no outlet. It is doubt- 



Peritoneol funnels 

 (persistent nephrostomes) 



Persistent nephrostomes oi the frog. (A) Ventral face of the frog kidney 

 showing the persistent peritoneal (nephrostomal) funnels which drain the 

 body cavity fluids directly into the venous sinuses. Note the nearby adrenal tissue. 

 (B) High power surface view of the kidney. (C) Section through a peritoneal 

 (nephrostomal) funnel. 



