134 



CEPHALOCHORDATA 



up. A depression on the floor of the enteron close to the mouth 



mr 

 ch 



sv 



FIG. 86. A, young larva of Amphioxus. B, anterior end enlarged, c, Provisional 

 tail-fin ; ch, notochord ; en, neurenteric canal ; d, enteron ; h, coelom of snout ; A', 

 club-shaped gland ; k' its external aperture ; ks, first gill-slit ; m, mouth ; mr, 

 nerve -tube; np, neuropore ; sv, sub-intestinal vein; w, pre-oral pit. (After 

 Hatschek. ) 



aa, 



Fio. 87. More advanced larva of Amphioxus. an, Anus ; au, eye-spot ; c, larval tail- 

 fiu ; ch, notochord ; d, enteron ; fl, rudiment of endostyle ; k club-shaped gland ; 

 k', its external aperture ; m, mouth ; np, neuropore ; w, pre-oral pit ; x, 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- 



