EXTERNAL CHARACTERS 



115 



(caudal fin, cd.f), and then forwards along the upper surface 

 (dorsal fin, dors.f) to the anterior end of the body. These fins 



Fig. 69. — Amphioxus {Branchiostoma lanceolalum) in the Pantano at Messina. 

 (After Willey.) 



thus constitute a continuous median fold around a great part of 

 the animal (Fig. 70, B, and Fig. 71). 



Fig. 70. — Branchiostoma lanceolatitm. A, ventral ; B, side view of the entire animal. 

 an. Anus ; atrp, atriopore ; cd.f, caudal fin ; cir, eirri ; dors.f, dorsal fin ; dors.f. r, 

 dorsal fin-rays ; gon, gonads ; intjil, metapleure ; myom, myomeres ; noli, noto- 

 chord ; or.hd., oral hood: vent.f, ventral fin; ventf.r, ventral fin -rays. (After 

 Kirkaldy.) 



The surface is soft all over, there being no exoskeleton. 

 The epidermis or ectoderm is formed by a single layer of 



