6F 



OS 



BR.1 



BR.2 



KA 



KA 



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

 OF HATCHING. (After Marshall.) 



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

 B R.I, SR.2, BR3, first, second, and third branchial arches. C, body-cavity or 

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

 bular gill-pouch. H K, hy old arch. IN, infundibulum. KA, archinephric duct 

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

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

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

 geal region of mesenteron. TI, intestinal region of mesenteron. V, yolk-cells. 



59 



