372 TUNICATA. 



torn (fig- 175, g), which carries them, without any effort of swal- 

 lowing, towards the stomach. 



(406.) The oesophagus (Jig- 175, h) is short, and internally 

 gathered into longitudinal folds. The stomach (i) is simple, mode- 

 rately dilated, and has its walls perforated by several orifices, through 

 which the biliary secretion enters its cavity. The liver is a glandular 

 mass intimately adherent to the exterior of the stomach and the 

 intestinal canal (Jig. 174, e, e), of variable length and more or 

 less convoluted in different species, after one or two folds, termi- 

 nates in the rectum, which, emerging from the peritoneal invest- 

 ment covering the intestine, has its extremity loosely floating in the 

 cavity communicating with the second orifice (f) : into the latter a 

 bristle is introduced in the figure, having its extremity inserted into 

 the anal extremity of the digestive tube. Excrementitious matter, 

 therefore, when discharged from the rectum, escapes from the body 

 through the common excretory aperture generally situated upon 

 the least elevated protuberance of the outer covering.* It would 

 seem that the food of Ascidians consists of very minute particles 

 of organized matter ; for, although small Crustacea and other animal 

 remains have been occasionally met with in the branchial cham- 

 ber, nothing of this nature has been observed in the stomach 

 itself, and, as must be obvious to the reader, the oral aperture 

 seems but little adapted to the deglutition of bulky substances. 



(407.) The reproductive system in these humble forms of Mol- 

 lusca presents the utmost simplicity of parts ; being composed of 

 an .ovarian nidus, in which the germs of their progeny are ela- 

 borated, and a duct, through which their expulsion is accomplished. 

 Nothing resembling a male apparatus has been satisfactorily indi- 

 cated ; and consequently, if in this form of hermaphrodism the 

 provision of an impregnating fluid be really indispensable to the 

 fertility of the ova, we must suppose it to be furnished by the 

 walls of the egg-passages themselves. The ovary is a whitish 

 glandular mass embedded with the liver among the folds of the 

 intestine : its position injtfg. 174 is indicated by the letter m ; and 

 at o, Jig. 175, it is seen separated from the surrounding struc- 

 tures. The oviduct, which is occasionally very tortuous, accom- 

 panies the rectum, and terminates near the anal aperture {Jig- 174, 

 m, Jig. 175, o), so that the ova ultimately escape through the 

 common excretory orifice. 



(408.) Deprived as these animals are of any of the higher organs 



* Cuvier ; M6moire sur les Ascidies, p. 14. 



