^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 j*^^' 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 am'icle 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. 



HI. 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. 



^ 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 naturaUst asserts 

 (Symb. physic, animal, evertebr. Mollusca), cannot 

 be determined except from a most exact analysis 

 of these organs. Troschel {Wiegmami's Arch. 

 1845, I. p. 197, Taf. VIII.) has shown with more 

 certainty that Ainpullaria is amphibious, for he 

 found a pulmonary above the branchial cavity 

 communicating with this last, and lined with blood- 

 vessels. 



3 With Limax, 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, Limax, &e. ; see Cuvier, M6m. 

 loc. cit. PI. n. fig. 8-10 (Arion). 



6 See Cuvier, Ibid. PI. 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 Erdl (De Helicis algirae, &c., 

 fig. 6, copied in Cams, Erläuterungstafeln, Taf 

 II. fig. 10) has figured with many details, all the 

 vascular trunks do not run towards the principal 

 vein, but with some their large extremity is directed 

 towards the border of the lungs. 



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 ; see 

 his Anat. de I'HelLs algira, in the Ann. d. Sc. 

 Nat. V. 1836, PI. X. fig. 3, f.* 



* [ 5 221, Dote 6.] See, for the respiratory organs of the terrestrial Gasteropola, ieirfy, loc. cit. p. 

 235. — Ed. 



uj( LIBRARY 



