174 CHORD ATA. 



5. Make thick free-hand sections of various regions and 

 study with a low power in a watch-glass, to supplement the study 

 of stained sections. 



6. Prepared sections should be studied that show the follow- 

 ing five regions: (a) buccal cavity; (6) anterior part of pharynx; 

 (c) posterior part of pharynx with gonads and liver; (d) atrio- 

 pore; (e) anus. 



The five sections should be studied with a low power and 

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

 limits of the ccclom 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 c&lom, 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. 



