134 CEPHALOCHORDATA CHAP. 
up. A depression on the floor of the enteron close to the mouth 
- See - 5 
lt a. 
SQ 
Fic. 86.—A, young larva of Amphioxus. B, anterior end enlarged. c, Provisional 
tail-fin ; ch, notochord ; cn, neurenteric canal; d, enteron; h, coelom of snout ; /, 
-club-shaped gland; hk’ its external aperture; Xs, first gill-slit; m, mouth; mv, 
nerve-tube; np, neuropore; sv, sub-intestinal vein; w, pre-oral pit. (After 
Hatschek. ) 
Fic. 87.—More advanced larva of Amphioxus. an, Anus; au, eye-spot ; ¢, larval tail- 
fin ; ch, notochord ; d, enteron ; fl, rudiment of endostyle ; /, club-shaped gland ; 
k’, its external aperture ; m, mouth ; np, neuropore ; w, pre-oral pit ; 2, provisional 
nephridium ; 1-4, gill-slits. (From Korschelt and Heider, after Lankester and 
Willey.) 
gives rise to the “ club-shaped gland” (Fig. 86, B, %), which is 
probably a gill-cleft in its nature. 
The walls of the coelomic pouches, which have been extend- 
ing both dorsally and ventrally (Fig. 84, D), become the meso- 
sete 
