230 



AETHUU WILLEY. 



of Amphioxus be legarded as vestigial structures, the impor- 

 tance of their possession of an internal opening is diminished. 



Fig. 1. — Diagram of anterior end of an Enteropneust, to show the regional 

 canals and pores. The proboscis-pores are indicated as they sometimes 

 occur in Ptychodera flava; the collar and truncal pores as in 

 Spengeiia. c. e. Anterior and posterior margins of collar, c. f. Collar 

 funnels, d. c. Dorsal canals of proboscis coeloni. e. v. End vesicles of 

 proboscis (Eichelpforten). g. p'. First gill-pores (only the most dorsal 

 portion of the first gill-pouch is indicated), p. c. Proboscis ccelom. 

 ph. Perilisemaf cavities. p. p. Proboscis-pores, t. c. Truncal canals 

 (opening with the collar canals into the first gill-pouch). 



In Ptychodera flava there are always two proboscis- 

 pores, one of which (either the right or the left) is smaller 

 than the other, and its terminal vesicle is usually not in 



usually does present peculiar vestiges of structures which were presumably 

 associated together iu the ancestral forms. 



