EXTERNAL CHARACTERS 



(caudal fin, c (/./), and then forwards along the upper surface 

 (dorsal fin, dors./} to the anterior end of the body. These fins 



FIG. 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). 



FIG. 70. Branchiostoma lanceolatum. A, ventral ; B, side view of the entire animal. 

 an, Anus ; atrp, atriopore ; rtl.f, caudal fin ; cir, cirri ; dors.f, dorsal fin ; dors.f.r, 

 dorsal fin -rays ; (/on, gonads ; mtpl, metapleure ; myom, myomeres ; nch, noto- 

 chord ; or.hcl, 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 



