OF 



6F 



OS 



BfU 



ecu 



FIG. 22. HORIZONTAL SECTION OF A TADPOLE AT THE TIME 

 OF HATCHING. (After Marshall.) 



AF, afferent branchial vessel of the first branchial arch. B F, fore-brain. 

 B R.I, B R.2, BR.3, first, second, and third branchial arches. C, body-cavity or 

 coelom. E F, efferent branchial vessel of first branchial arch, tf M, hyomandi- 

 bular gill-pouch. H V, hypid arch. 7^V, infundibulum. K A, archinephric duct 

 of right side. KA', archinephric duct of left side, seen in section. K P, head- 

 kidney or pronephros. KS, third nephrostome of right head-kidney. K S', same 

 of left side, seen in section. OF, olfactory pit. OS, optic stalk. TP, pharyn- 

 geal region of mesenteron. T ' f, intestinal region of mesenteron. Y, yolk-cells. 



59 



