.204 THE ACEPHALA. <§> 189. 



The intestinal canal is short, without a distinct stomach, and somewhat 

 spirally convoluted. '-' Its extremity opens by a large anal orifice near the 

 mouth. ^''' 



With the Ascidiae, the intestinal canal is quite distinct. The mouth is 

 situated in the respiratory cavity, far removed from the so-called oral tube, 

 or more properly speaking, the respiratory orifice. It is surrounded with 

 thick lips, and has at its posterior extremity with many species, a semi-canal 

 closely resembling, and undoubtedly of the same signification as the ventral 

 furrow of Salpa. This canal is formed by two narrow folds arising below 

 the circle of tentacles which surround the interior of the oral cavity ; it passes 

 along the large curvature of the respiratory cavity, and rising upon its oppo- 

 site side, ends, after a longer or shorter course, below the oral cavity.**' The 

 mouth opens into a short ossophagus, and this last ends in a long or round 

 stomach, which is often quite circumscribed and plicated longitudinally 

 on its inner surface.*^' The intestine passes first towards the base of the 

 body by a short arch, then by a longer one it rises towards the mouth, 

 and thence passes to the anal tube, opening, by a fringed anus, sometimes 

 close behind the mouth, and sometimes further below it.*"^ 



With the Brachiopoda, the mouth is simple and concealed between the base 

 of the two tentacular arms. With Terebratula, the oesophagus is very long and 

 curving, opening into a large stomach;*"' but with the other Brachiopoda, 

 the stomachal dilatation is wanting, and the intestine is simply convoluted. 

 With Orbicula, and Terebratula, the intestine is short, and has only a single 

 convolution which passes to the right and terminates in a lateral anus hid- 

 den between the lobes of the mantle. But with Liyigula, it is much longer, 

 and its turns are quite numerous ; the anus here is lateral also, and opens 

 through a small papilla which projects from the cavity of the body into 

 that of the mantle.'**' 



With the Lamellibranchia the intestinal canal is highly developed, but 

 always buried in the midst of other abdominal viscera. The mouth, situated 

 at the bottom of the cavity of the mantle, and beneath the anterior adduc- 

 tor muscles, is surrounded by two pairs of tentacles in the form of tactile 

 lobes ; these often form a furrow leading to the mouth, and along which pass 

 the particles of food drawn in by the cilia.*''' The mouth opens, either 



2 See Home, Lact, on Comp. Anat. II. PI. With PAaWusia ?"?i<fi.?<maZ!,9, there is, opposite 

 liXXII. {Halpa Tilesii). tliis canal ami upon the side of the respiratory cav- 



3 For tlie oral and anal orifices of Salpa, see the ity corresponding to tlie anal tube, a longitudinal 

 figures of Cuvier, and Savigny, loc. cit. Some row of very long thickly-set filaments, extending 

 species however differ from the descriptions here even to the oral aperture. Eschricht has seen a 

 given. Thus, according to a preparation in Hu7i- row of similar tentacles with C/ielyosoma ; see loc. 

 ter's MusL-um, the intestine of Salpa gibbosa has cit. p. 10, fig. 4, 6, z. 



two caecal appendages (Home, Luct. &c. PI. LXXI. 5 The stomach is elongated with Bo/tenia, Phal- 



tig. 2, 3, and Catalogue of the Phys. Series, I. p. lusia, Cynthia, SisciUina, and spherical with 



132, PI. VII. fig. 1, 2, i. i.). The intestinal canal Aplidium, Eucoelium, kc. Its longitudinal f.ilds 



<f Salpa pinnata presents a still more remarkable are often very distinctly marked externally by deep 



ixception. No nucleus is formed, but the mouth grooves, as is the case with Sigillinn, J/ilhliiim, 



»pens directly into the stomach which is curved and Botryllus ; see for this, Snrii^ny, Inc. cit. 



ftu'l sends off an intestine in front, and the anal According to him also there is a small caecum at 



orifice is situated near the anterior extremity of the the base of the stomach with Hotrytlus Srhlos- 



ventral groove ; see Cuvier, loc. cit. p. 11, fig. 2; seri, and polycyclus ; see M6m. kc. p. 201, PI. 



Home, loc. cit. PI. L.XXIII. fig, 2, and the Catalogue XX. fig. 5-, PI. XXI. fig. 1*, c. 



of the Phys. Series, I. PI. VI. fig. 4. U Uiion the course of the intestine with the Asci- 



i Savigny has described this canal with the most diae, see Cuvier, Savigny, and Home, loc. cit, PI. 



different Ascidians as a Sillon dorsal; see the L.XXIV. and the Catal. of the Phys. Ser. I. PI. V. 



figures (loc. cit. PI. VI. &c.) of Cynthia, Phallu- {Pliallusia). 



sia, Diazona, Synoicum, Aplidium, Eucoelium, 7 See the figure given by Owen, loc. cit. 



Polyr.linum, liutryltus, Pyrusoma, (fC. 8 For the intestinal canal of several Brachio- 



Caru.i also has called the attention to this canal poda, see Cuvier, Oiven, and yogt, loc. cit. 



with Cynthia viicrucoamu^ (Nov. Act. Acad. '■> \i\lh Cardium, Isocardia, Avicula,kc.,ü\esfi 



Physiüü-Med. loc. cit. p. 432, Tab XX\II. fig. 1, 2, two pairs of gustatory lol)ules are very distinctly 



<}•)• 8eeu passing towards the mouth by as many lateral 



