134 



CEPHALOCHORDATA 



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



mr ch 





^^Is^^^piCJgErESte^iSj^iiS 



B 



l^^-l ^ ^ n ,--^1Sl^si(-ffe^.-'^"^ — f- ' : — - ^ f- 



.-"■^-„ 



7u *=/--./; 



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 ; k, 

 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, ^P se 



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

 fin ; ch, notochord ; d, enteron ; /, rudiment of endostyle ; k, club-shaped gland ; 

 /.: , its external aperture ; m, mouth ; np, neuropore ; w, pre-oral pit ; cc, provisional 

 nephridium ; 1-4, gill-slits. (From Korschelt and Heider, after Lankester and 

 Willey.) 



gives rise to the " cluh-shaped gland" (Fig. 86, B, k), 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- 



