A Simple Tunicate. 139 



around the siphonal canal, just outside the peripharyngeal 

 bands. 



Drawings should now be made of the structures thus shown 

 on the interior of the pharynx. 



Carefully remove the ganglion together with the immedi- 

 ately surrounding tissues, and examine it carefully in a watch 

 glass. 



From its inner surface a funnel-shaped process will be 

 observed. This is the dorsal tubercle, and is a part of a 

 small glandular mass, the neural gland. The course of the 

 nerves can be readily determined by the adoption of the 

 xylol method described for the nervous system of the Phyl- 

 lopod Crustacea. 



Make a drawing of the ganglion and of its associated 

 structures. 



General Remarks. The outer covering of the Tuni- 

 cates is variously described as the test, tunic, outer mantle, 

 or sac. It varies considerably in different types, being in 

 some delicate and transparent, in others tough and opaque. 

 It is produced by the activity of a lining layer of epithelial 

 cells, and is consequently comparable with the covering of 

 many Invertebrates. It is peculiar in that it contains cellu- 

 lose. The mantle or muscular sac (integument, second or 

 inner muscular tunic) is also subject to considerable varia- 

 tion. In life it is attached throughout to the inner surface 

 of the tunic, though in alcoholic specimens it is often 

 partially free. 



The Digestive System. Food that is drawn into the 

 pharyngeal sac by the activity of the cilia of the pharyngeal 

 walls is collected by the mucus secreted, probably by the 

 endostyle or by the sub-neural gland, and is carried along 



