their Tood and Digestive Organs, 219 



when the animal was left undisturbed. I presume them to be 

 organs of a very delicate irritability, perhaps of taste* ; and 

 that their purpose is to hinder the ingress of noxious matters, 

 not altogether mechanically, but because the sudden contrac- 

 tion of the oral aperture is a necessary sequence of their 

 unpleasant irritations.f This aperture leads directly into the 

 branchial sac, which, besides its office of a respiratory organ, 

 seems to perform in part that also of a stomach ; for that the 

 process of digestion commences there, seems obvious from the 

 fact, that numerous animalcules are generally found in it, but 

 are never to be detected in the viscera of the abdomen. At 

 the base of this sac there is another aperture (called by Cuvier 

 the mouth), which conducts us, through the medium of a 

 narrow membranous tube or oesophagus, into the proper sto- 

 mach : an organ always much smaller than the branchial sac, 

 very variable in point of situation and form, generally puckered 

 into longitudinal plaits internally, and sometimes studded with 

 some glandular bodies; but its minute structure cannot be 

 ascertained with any degree of accuracy. It contains, in 

 general, only a little liquid J ; while the intestinal canal, on 

 the contrary, is almost, in every instance, filled throughout 

 with a sufficiently consistent matter, sometimes grumous, 

 more often homogeneous, of a yellowish grey colour, and 

 rolled into little round or egg-shaped pellets, which it behoves 

 us not to mistake for the proper ova. This canal is usually 

 wide, and has a flexuous course ; at first descending in the 

 common sac, and then returning upon itself, it winds along 

 the anterior side of the branchial sac, to open outwardly by a 

 round aperture placed near the mouth, but distinguished by 

 its lesser prominence. In the ^Icy^nese, it is otherwise like 

 the mouth in form and structure ; but, in Ascidise, there is no 

 filamentous fringe at this orifice ; which is furnished, instead, 

 either with two valvular folds, or with a simple circular plait. 

 In many of the solitary Ascidiae, the stomach is enveloped 

 in a large liver §, which pours the bile directly into it through 



* " The disposition of the alimentary canal determines, in a manner 

 perfectly absolute, the kind of food by which the animal is nourished; but 

 if the animal did not possess, in its senses and organs of motion, the means 

 of distinguishing the kinds of aliment suited to its nature, it is obvious it 

 could not exist." (Cuvier, Comp. Anat.y vol.i. p. 55. trans.) 



f " II est garni d'une rangee de filamens charnus, ou de tentacules tres- 

 fins, qui servent sans doute a I'animal pour Pavertir des objets nuisables 

 qui pourroient se presenter et qu'il doit repousser." (Cuvier, Mem., xx. 

 p. 10.) 



J From this circumstance Savigny infers that the more gross and indi- 

 gestible parts of the food are regurgitated, as they are in some nocturnal 

 birds of prey. (^Mem. sur les Animaiix sans Vert., vol.ii. p. 8.) 



§ In Boltenia there is no liver. (Savigny's Mem., vol. ii. p. 88.) 



