AMPHIOXUS LANCEOLATUS. 185 



ACRANIA. 



AMPHIOXUS LANCEOLATUS. 



While living material is not easily provided for laboratory 

 work, it should be understood that this form spends most of its 

 time in the sand of the bottom, in which it burrows with great 

 ease by movements of the body. 



1. In an alcoholic specimen note the dorsal, ventral, and 

 caudal regions of the median fin, metapleural folds, muscle plates 

 or myotomes, buccal cavity fringed with cirri, atriopore, and anus. 



2. Using a specimen that has been macerated in 20 percent 

 nitric acid, remove the skin and myotomes from the right side 

 very carefully, by means of needles, -exposing the not ochord, 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 Amphionus one centimeter 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 "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 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. 



