THE ASCIDIA. 41 



water can be expelled through the same orifice in 

 a considerable stream. At the bottom of this re- 

 markable sac is the mouth of the animal, a simple 

 orifice leading to a short gullet, and open to receive 

 whatever alimentary particles are taken into the respi- 

 ratory sac with the water imbibed. These particles, 

 being deposited on the inner surface of the sac, are 

 conveyed in a stream down the front of the cavity by 

 the action of the cilia, and entering the oral orifice, pass 

 into the stomach. 



This organ is simple, and admits through tubes the 

 secretion of the liver, which organ adheres to its sur- 

 face, and to that of the adjacent part of the alimentary 

 canal. The alimentary canal varies in length, and the 

 number of its convolutions, in different species ; it is 

 attached to a membrane, and terminates in a cavity, 

 communicating with the orifice b. The annexed dia- 

 gram will convey a clear idea of the visceral arrange- 

 ments described, a, the imbibing orifice ; b, the ex- 

 cretory orifice ; c, c, the external tunic or sac in which 

 the body is inclosed, laid open ; d, the muscular tissue 

 covering the body laid open, so as to expose the mem- 

 brane of the aerating cavity, e, also laid open to show the 

 true mouth at f, leading to the stomach and intestinal 



