$ 222. THE CEPHALOPHORA. 251 
at the anterior part of the back, rarely at the posterior part. Its ori- 
fice, which can be closed by a kind of sphincter, is upon the right side ; it 
is upon the left with those species only which have sinistral shells, and in 
one genus alone, it is upon the median line at the posterior extremity of 
the body.” The pulmonary cavity is triangular with those species which 
have a shell, and round with those which are without it.© Its interior is 
lined with a raised vascular net-work which, with the aquatic species, is 
covered with a ciliated epithelium.” With the naked Gasteropoda, this 
net-work forms a uniformly-meshed trellis ;® while with the others, there 
may here be usually seen several large pulmonary veins, which, in passing 
towards the middle principal vein, are spread over’ the borders of the 
respiratory cavity, frequently anastomose with each other, and receive 
several other veins of a dendritic form. The principal vein opens, at last, 
into the auricle of the heart at the posterior corner of the pulmonary 
cavity. 
Carefully examined, these veins will be found to be wall-less canals 
directly surrounded by the transverse and longitudinal fibres of the man- 
tle, so that, apparently, they are only a continuation of the venous canals 
of the walls of the body. 
III. Aquiferous System. 
§ 222. 
The existence of aquiferous vessels and reservoirs, with the Cephalo- 
phora, is not yet satisfactorily settled. However, it appears that here, as 
with the Acephala, there is an aquiferous system with wall-less canals, of 
which some are singly ramified, while others form an anastomotic net-work, 
but all accompany the venous canals and open upon the surface of the 
body, — presenting an arrangement analogous to the trachean system of 
insects. 
With some Apneusta, the existence of this system, which may have the 
function of an internal respiratory apparatus, can scarcely be doubted ; 
1 The respiratory cavity is situated in the middle 
of the back with Parmacella, and wholly behind 
with Testacella, and Onchidium. 
2 Onchidium. Whether or not the contractile, 
ramified excrescences at the posterior part of 
the back of this amphibious mollusk, of which 
Ehrenberg has counted more than twenty, serve 
really as branchiae as this naturalist asserts 
(Symb. physic. animal. evertebr. Mollusca), cannot 
be determined except from a most exact analysis 
of these organs. T'roschel (Wiegmann’s Arch. 
1845, I. p. 197, Taf. VIII.) has shown with more 
certainty that Ampullaria is amphibious, for he 
found a pulmonary above the branchial cavity 
communicating with this last, and lined with blood- 
vessels. 
8 With Limaz, and Arion, the respiratory cav- 
ity has an annular form, its centre being occupied 
by the heart and kidney. 
4 I have found ciliated epithelium in the pulmo- 
nary cavity of the Lymnaeacea, but not in that of 
Helix or Arion. 
5 Onchidium, Limaz, &e. ; see Cuvier, Mém. 
loc. cit. Pl. II. fig. 8-10 (Arion). 
6 See Cuvier, Ibid. Pl. I. fig. 2-4, and Trevi- 
ranus, Beobacht. aus. d. Zoot. u. Physiol. Tab. 
VIII. fig. 57, 58 (Helix pomatia). In the vascu- 
lar net-work which Erdi (De Helicis algirae, &c., 
fig. 6, copied in Carus, Erlauterungstafeln, Taf 
II. fig. 10) has figured with many details, all the 
vascular trunks do not run towards the principat 
vein, but with some their large extremity is directed 
towards the border of the langs. 
This disposition, however, does not exist in na- 
ture. The pulmonary vessels of this species are 
arranged like those of Helix pomatia, which is 
also confirmed by Van Beneden’s figure of it 5. see 
his Anat. de PHelix algira, in the Ann. d. Sc. 
Nat. V. 1836, Pl. X. fig. 3, £.* 
* (§ 221, note 6.] See, for the respiratory organs of the terrestrial Gasteropoija, Leidy, loc. cit. p. 
235. — Ep. 
