^ 222. THE CEPHALOPHORA. 251 



at the anterior part of the back, rarely at the posterior part/^' Its ori- 

 ^ce, 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 Crasteropoda, 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 nary cavity of the Lymnaeacea, but not In that of 

 of the back with Parmacella, and wholly behind Helix or Arion. 



with Testacella, and Onchidium. ' 5 Onchidium, Limax, &c. ; see Cuvier, M6m. 



2 Onchidium. Whether or not the contractile, be. cit. PI. U. fifi. 8-10 (Arion). 



ramified excrescences at the posterior part of 6 gee Cuvier, BM. PI. I. fig. 2-4, and Trevi- 



the back of this amphibious moUusk, of which ranus, Beobacht. aus. d. Zoot. u. Physiol. Tab. 



Ehrenberg has counted more than twenty, serve VIII. fig. 57, 58 {Helix pomatia). In the vascu- 



really as branchiae as this naturalist asserts lar net-work which Erdl (De Ilelicis algirae, &c., 



(Symb. physic, animal, evertebr. MoUusca), cannot fig. 6, copied in Cams, Erlauterungstafeln, Taf. 



be determined except from a most exact analysis II. fig. 10) has figured with many details, all the 



of these organs. Troschel (fViegmann's Arch, vascular trunks do not run towards the principal 



18-15,1. p. 197, Taf. VIII.) has shown with more vein, but with some their large extremity is directed 



certainty that Ampullaria is amphibious, for he towards the border of the Ivuigs. 



found a pulmonary above the branchial cavity This disposition, however, does not exist in na- 



communicating with this last, and lined with blood- ture. The pulmonary vessels of this species are 



vessels. arranged like those of Helix pomatia, which is 



3 With Limax, and Arion., the respiratory cav- also confirmed by Fan Beneden^s figure of it ; see 

 Ity has an annular form, its centre being occupied his Anat. de I'HeUx algira, in the Ann, d. Sc. 

 by the heart and kidney. Nat. V. 1836, PI. X. fig. 3, f.* 



4 I have found ciliated epithelium in the pulmo- 



* [ \ 221, note 6.] See, for the respiratory organs of the terrestrial Gasteropoda, Leidy, loc. cit. p. 

 235. — Ed. 



