IV EXTERNAL CHARACTERS TOD IAGS 
(caudal fin, cd.f), and then forwards along the upper surface 
(dorsal fin, dors.f) to the anterior end of the body. These fins 
Fia. 69.—Amphioxus (Branchiostoma lanceolatum) 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). 
A 
B MYON de or. 
Fic. 70.—DLranchiostoma lanceolatum. A, ventral; B, side view of the entire animal. 
an, Anus ; atrp, atriopore ; cd.f, caudal fin ; civ, cirri; dors.f, dorsal fin ; dors.f.7, 
dorsal fin-rays; gon, gonads; mtpl, metapleure ; myom, myomeres ; nch, noto- 
chord ; or.Ad, oral hood: vent, ventral fin; vent fr, 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 
