186 CHORDATA. 



The five sections should be studied with a low power and 

 drawn. In (6) (anterior part of pharynx), note especially the 

 limits of the coelom and atrium, the lymph-spaces in the meta- 

 pleural folds, the two dorsal aortce, the ventral aorta, the epibran- 

 chial groove, the endostyle, the sub-endostylar coelom, and the two 

 kinds of gill-bars, primary and tongue-bars. 



With a high power study the nerve cord (best shown in re- 

 gion a) and the gill-bars and endostyle (best shown in region 6). 



Drawings of these regions are desirable. 



Willey: Amphioxus and the Ancestry of Vertebrates. Columbia Univ. 

 Press. 



