196 OUTLINES OF CHORDATE DEVELOPMENT 



nearly filled by them. Each tubule carries around it a reflected 

 layer of the thin vascular wall and so is completely bathed in 

 the venous stream (Fig. 72). 



cv 



FIG. 72. Sections through frog larvae illustrating the later development of 

 the pronephros. A. Through the first nephrostome of a larva of R. syhatica of 

 about 8 mm., with prominent external gills. After Field. B. Through the region 

 of the second nephrostome of a 12 mm. larva of R. temporaria. After Furbringer. 

 c, Coelom; cv, sinuses of posterior cardinal vein; eg, external glomerulus; g, gut 

 cavity; gX, ganglion nodosum (part of the ganglion of the vagus nerve) ; I, lung; 

 TO, mesenchyme; myz, second myotome; p, peritoneum; si, sz, first and second 

 pronephric nephrostomes; tr, common trunk; X, root of vagus nerve. 



At the same time an arterial supply is derived from the 

 dorsal aorta. This is the pronephric glomus already mentioned. 



