TUNIC AT A. 271 



orifice at the bottom of this cavity conducts by a short oesophageal 

 canal to the stomach, an oblong dilated sac, with longitudinal folds. 

 The intestine is disposed in a sigmoid flexure, adheres to the branchial 

 and muscular sac, and terminates by an anal aperture near the base 

 of the second orifice of the tunic. 



A simple follicular liver is developed from the stomach. In the 

 Cynthia tuberculata it communicates with the stomach by a single 

 aperture, from which a groove is continued towards the cardia. 



A generative gland, generally dendritic in shape, occupies the 

 concavity of the intestinal fold, and sends a short and simple duct to 

 terminate near the anus. In the female Cynthia tuberculata there are 

 two ramified ovaria ; the ovisacs being appended to the branches of a 

 central stem, passing up by the side of the rectum, and extending over 

 one side of the branchial sac. 



The heart is a simple, elongated, vasiform muscle, inclosed in a 

 pericardium, attached to the branchial sac ; continued at either end 

 into a vessel ; the ramification of one being expended chiefly upon 

 the respiratory organ ; those of the other upon the viscera and tunics 

 of the body. According to the direction of the circulating currents 

 the one will be an artery, the other a vein, and the circulation itself 

 will be pulmonic and systemic. 



The nervous system must be first sought for in the interspace 

 between the two openings of the muscular tunic ; there you will find 

 a ganglion from which it is not difficult to trace filaments diverging 

 to each aperture of the sac where the circular disposition of the 

 muscular fibres prevails ; other branches accompany the longitudinal 

 fibres, and supply the respiratory sac ; two contiguous filaments are 

 continued to the oesophageal orifice. 



In the animal manifesting this organisation, which is much richer 

 unquestionably than the amorphous and rugged exterior would seem 

 to promise, the only vital actions obvious to ordinary vision are an 

 occasional ejection of water from the orifices of the tunic by a sudden 

 contraction, succeeded by a slow and gradual expansion. Such 

 contractions and expansions, aided by the ciliary currents, which the 

 microscope has detected, and the peristaltic movements of the ali- 

 mentarj', circulating, and secerning tubes, are all the actions which the 

 organic machinery has to perform in the living ascidian. 



The respiratory currents of sea water with the nutrient molecules 

 in suspension are introduced by the ciliary action through the 

 branchial orifice into the pharyngeal respiratory sac, from which the 

 oesophagus selects the appropriate food. The alimentary excretions 

 and the generative products are expelled through the anal outlet by 

 the contraction of the muscular tunic. 



