244 CHORDATA 



right side very carefully, by means of needles, exposing the 

 notochord, nerve cord, gonads, and the entire alimentary 

 canal (pharynx, intestine, and digestive diverticulum or 

 "liver," which lies along the right side of the pharynx) . 



3. Examine microscopically and notice: 



(a) The nerve cord, cerebral vesicle, cerebral nerves, eye 

 spot, and pigment cells. Note also the alternate metamerism 

 of the spinal nerves. 



(6) The buccal skeleton. 



(c) A large piece of the pharyngeal wall. 



4. Examine an Amphioxus 1 cm. in length, stained and 



mounted. 



Identify as many as possible of the structures mentioned 

 above, and in addition note: the olfactory pit, oral velum 

 with velar tentacles, and a taste organ" in the buccal cavity. 



A drawing showing the general structure is desirable. 

 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 fol- 

 lowing five regions: (a) buccal cavity; (b) anterior part 

 of pharynx; (c) posterior part of pharynx with gonads and 

 liver; (d) atriopore; (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 coelom and atrium, the lymph spaces in the 

 metapleural folds, the two dorsal aortae, the ventral aorta, 

 the epibranchial groove, the endostyle, the subendostylar 

 coelom, and the two kinds of gill bars, primary and tongue 



bars. 



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

 region a) and the gill bars and endostyle (best shown in re- 

 gion b). 



Drawings of these regions are desirable. 



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

 Press. 



