^190. 



THE ACEPHALA. 



205 



directly, or by a short oesophagus, ^"^ into a large stomach lined with numer- 

 ous papillae and apparently perforated by many biliary canals. The 

 intestine, when short, forms a single arch only ; but when long, it has many 

 convolutions ; it terminates in a rectum which lies along the dorsal surface 

 of the abdomen,^"' and passes between the lobes of the mantle, under the 

 hinge and above the posterior adductor muscle, finally terminating above in 

 a ciliated anus, situated upon a small prominence/^-* With the majority 

 of this order, the rectum traverses the heart. ^^'> There is often, near the 

 pylorus, a long caecum^"' extending between the convolutions of the intes- 

 tine to the lower extremity of the abdomen, and which contains, through its 

 whole extent, a cylindrical transparent cartilaginoid body — the so-called 

 crystalline-stalk. ^^'^ A longitudinal fold extends along the inner surface 

 of the entire intestine and a large part of that of the rectum, and thereby 

 the intestinal surface is increased. 



§ 190. 



The anterior portion of the digestive canal of the Acephala is entirely 

 without a Salivary glavd}^^ The Liver, however, is always present; it is 



grooves, whose borders as already mentionod 

 ( § 185) are blended above and below with the oral 

 orifice. With Pectunculus, and Area, there is a 

 still more remarkable arrangement. 



Theii- lobules of this kind consist only of two 

 narrow folds upon each side of the mouth, and be- 

 tween which is a transverse furrow, resembling the 

 ventral-groove of Salpa, or the semi-canal of the 

 Ascidiae. The important part which this appara- 

 tus serves in the prehension of food, can be seen 

 by covering those of Anodonta and Unio with a 

 powdered colored substance. 



This powder is carried by cilia from the surface 

 to the borders of the tentacles, thence upon their 

 transversely grooved internal surfaces even into the 

 angle formed by these last, thence into currents of 

 the grooves, and so direct into the mouth. 



10 A distinct but short oesophagus is found with 

 Area. Cha7na, Pinna, Cardium, and Mactra. 



11 The intestine is short and has a single arch 

 with Spondylus, Pecten, Area, and Cliama. It is 

 long and has many turns with Pholas, Tellina, 

 Cardium, Maetrq, Pinna, Ontrea, &c. 



12 The anus is short and situated directly behind 

 the anal fissure of the mantle with Unio, Ano- 

 donta, Cardium, Isocardia, &c. ; while with As- 

 per^illum, Lutraria and Solen, it is situated far 

 removed from the siphon. With Area, Pectuncu- 

 lus. Pinna, and Avieula, the rectum passes 

 around a large portion of the adductor muscle and 

 ends in front in a papilla, which, in the last* two 

 genera is quite long. With Lima, it ascends a 

 Uttle way along the anterior surface of the adduc- 

 tor muscle, and with Pee ten and Ostrea, it leaves 

 the median line upon the back of this muscle and 

 passes obliquely towards the smaller valve. 



13 To this. Area, Ostrea, and Teredo, form an 

 exception, and especially with the last, where the 

 intestinal canal is distinguished for several other 

 peculiarities. Thus, the stomach is double and 

 anteriorly divided to its base by a longitudinal sep- 

 tum ; see Home, Lect. &c. PI. LXXX., and Des- 

 hayes. Comp. Rend. 1846, XXII. No. 7 ; or Fro- 

 riepK'i neue Not. No. 813. 



14 For the caecum of So/en, Mactra, and Car- 

 dium., see the figures of Garner, On the Anat. of 

 the Lamellibr. &c. PI. XVIII. fig. 8-10 ; and for 

 the disposition of the intestinal canal in general, 

 *ee the Plates of Poli, loc. cit. 



18 



According to Owen (Anat. of Clavagella, &c., 

 PI. XXX. flg. 16, r.), Clavagella has a very short 

 and rudimentary caecum. 



15 With the exception of Anomia, the crystalline 

 stem is wautmg in all the Monomya {Garner, loc. 

 cit. p. 89). But it exists with many Dimya, as 

 Pholas, Solen, Area, Mactra, Vonax, CarUiinn, 

 Tellina, Anodonta, Unio, Mya, &c. ; see Poli, 

 loc. cit. Tab. VII. XIII. XIV. XVI. XIX. XX. 

 XXIV. With many of these, there is no caecum 

 and the crystalline stem is situated in the intestine 

 itself. It has always a cylindrical form, and is of a 

 decreased size at its lower end, while at the oppo- 

 site one it is usually divided in several irregular 

 lobes which project into the cavity of the stomach 

 and appear to close up the orifices of the biliary 

 canals. With the Naiades, where the caecum is 

 wanting, I have found this singular body, which 

 extends from the stomach into the intestine, com- 

 posed of a cortical and a medullary portion. The 

 first which forms a kind of tube, is homogeneous, 

 transparent, and formed of concentric layers of the 

 consistence of the white of an egg. The second is 

 equally homogeneous and transparent, but is of a 

 more gelatinous nature and contains a quantity of 

 small granules (Unio), or batons (Anodonta), in- 

 soluble in acid, whicli, at the points where most 

 aggregated, give this organ a whitish color when 

 examined by reflected light. According to Poli's 

 description and figure of this organ with Pholas 

 dactylics, it has an analogous structure with the 

 other Lamellibrancliia (loc. cit. I. p. 47, Tab. 

 VII. fig. 11). As yet nothing positive can be said 

 of the function of this organ. It may be also added 

 that often with some individuals it is looked for ia 

 vain, while with others it is very distinct though 

 variable as to its development and the number of 

 layers composing its cortical portion. Hence it 

 seems that it disappears at certain times, to be 

 developed anew. 



That of Anodonta as figured by Bojanus (Isis, 

 1827, Taf. IX. fig. 9, 10) was undoubtedly in the 

 state of being formed, or disappearing. 



1 Cuvier (Sur la Lingule, loc. cit. p. 7, fig. 10, 

 11, a.), and Vogt (loc. cit.) have regarded the gland- 

 ular mass which, with Lingula, opens into the di- 

 gestive canal, as a solitary organ. But Owen (loc. 

 cit.) is opposed to this view and says that all the 



