§ 190. 205 
directly, or by a short cesophagus,™ 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 mautle, 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 
erystalline-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. 
THE ACEPHALA. 
§ 190. 
The anterior portion of the digestive canal of the Acephala is entirely 
without a Salivary gland.” The Liver, however, is always present; it is 
grooves, whose borders as already mentioned 
(§ 185) are blended above and below with the oral 
orifice. With Pectunculus, and Arca, there is a 
still more remarkable arrangement. 
Their 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 cesophagus is found with 
Arca, Chama, Pinna, Cardium, and Mactra. 
11 The intestine is short and has a. single arch 
with Spondylus, Pecten, Arca, and Chama. It is 
long and has many turos with Pholas, Tellina, 
Cardium, Mactra, Pinna, Ostrea, &e. 
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- 
pergillum, Lutraria and Solen, it is situated far 
removed from the siphon. With Arca, Pectuncu- 
lus, Pinna, and Avicula, the rectum passes 
around a large portion of the adductor muscle and 
ends in frontina papilla, which, in the last two 
genera is quite long. With Lima, it ascends a 
little way along the anterior surface of the adduc- 
tor muscle, and with Pecten and Ostrea, it leaves 
the median line upon the back of this muscle and 
passes obliquely towards the smaller valve. 
18To this, Arca, 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. Pl. LXXX., and Des- 
hayes, Comp. Rend. 1846, XXII. No. 7; or Fro- 
riep’s neue Not. No. 813. 
14 For the caecum of Solen, Mactra, and Car- 
dium, see the figures of Garner, On the Anat. of 
the Lamellibr. &c. Pl. XVIII. fig. 8-10; and for 
the disposition of the intestinal canal in general, 
see the Plates of Poli, loc. cit. 
According to Owen (Anat. of Clavagella, &c., 
Pi. XXX. fig. 16, r.), Clavagelia has a very short 
and rudimentary caecum. 
15 With the exception of Anomia, the crystalline 
stem is wanting in all the Monomya (Garner, loc. 
cit. p. 89). But it exists with many Dimya, as 
Pholas, Solen, Arca, Mactra, Donaz, Cardium, 
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 stumach 
and appear to close up the orifices of the biliary 
canals. With the Naiades, where the caecum is 
wanting, Ihave 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, which, at the points where most 
aggregated, give this organ a whitish color when 
examined by reflected light. According tu Poli’s 
description and figure of this organ with Pholas 
dactylus, it has an analogous structure with the 
other Lamellibranchia (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 in 
vain, while with others itis 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 Linguda, opens into the dix 
gestive canal, as a solitary organ. But Owen (loc. 
cit.) is opposed to this view and says that all the 
