•^^ 188, 189. THE ACEPHALA. 203 



CHAPTER V. 



DIGESTIVE APPARATUS. 



§ 188. 



The digestive canal of the Acephala is formed, throughout the class, upon 

 a single plan. It always consists of irregular convolutions which are sepa- 

 rated with difficulty, for their walls are generally not covered by a peritoneal 

 envelope, but are intimately blended with contiguous organs and especially 

 the liver and genital gland. The oral and anal openings, which are always 

 present, are not upon the surface of the body, but are situated in a cavity 

 circumscribed by the mantle.''' 



The mouth has always tumid lips and often tentacular appendages. Its 

 cavity has neither distinct nmscular walls, nor any trace of a masticatory 

 apparatus. It passes either directly, or by a short oesophagus, into a kind 

 of stomach which gradually contracts 'into a longer or shorter intestine, 

 scarcely difi'erent from it in its intimate structure. The extremity of the 

 intestine often projects into the cavity of the body, as a kind of papilla, 

 upon the end of which the anus is situated. Internally, this canal is lined 

 throughout with a very distinct, ciliated epithelium. 



The food of these animals, which consists of slime and small organized 

 bodies, is taken into the cavity of the body with the water, and is conduct- 

 ed to the mouth by the ciliated epithelium which lines this last. In a sim- 

 ilar manner the faeces are rejected with the refuse water. 



§ 189. 



The very feebly-developed digestive canal of Salpa consists only of a 

 small knob [Nucleus) situated in the posterior part of the cavity of the 

 body. It connects with a furrow formed by two narrow folds situated 

 along the ventral median line. 



This furrow may become a canal by the joining of its borders, and its 

 posterior extremity, which is a little lateral, opens directly at the entrance 

 of the intestinal canal which is surrounded with a lip, and ought therefore 

 to be regarded as a mouth. The folds of this furrow arise directly behind 

 the anterior respiratory orifice, and are very probably covered with cilia, 

 by which, solid particles of food taken into the body during respiration, are 

 borne towards the mouth. ''' 



1 With many Acephala, as with the Ascidiae and 1, 2, I.), and Eschricht (Over Salperne, p. 26, 

 Salpinae wliose mantle is entirely closed with the fig. i, S, ]8, m.) ; but they describe it as a dor- 

 exception of the two respiratory orifices, it is only sal furrow and a dorsal fold, for they have taken 

 in an improper manner that the terms oral and the abdominal cavity of these animals for the back, 

 anal can be ^'iven to these orifices. That of Salpa gibbosa is quite distinctly figured in 



1 With 5a//)a cordf/brmw, and TnaxjOTO!, I have the Catalogue of the Physiological Series, &c., I. 



seen tliis furrow quite distinctly. It appears to be PI. VII. fig. 1, k. This furrow corresiionds, pi-ob- 



present in all species. Cuvier has already men- ably, less to an open oesophagus, than to the ten- 



tioned and figured it (Mem. sur lesThalides, &c., tacle-furrow which, with all the LamellibrancU- 



p. 12, fig. 1, 2, 3, &c., 1/'.), and it has also been no- ia, is situated upon tlie two sides of the mouth. 

 ticed by Savigni/ (Mem. &c. p. 124, PI. XIV. fig. 



