248 



THE CEPIIALOPHORA. 



^219. 



opens into the veins, but gradually disappear,''" 80 that it is probable that 

 the blood is effused IVom their open extremities into the interstices of the 

 parenchyma of the viscera, as well as into the cavity of the body ; and is 

 thence taken up through numerous orifices on the inner surface of this last, 

 and conducted to the respiratory organs through the wall-less venous canals 

 which are hollowed iu the muscular substance of the envelope of the 

 body.'^* 



CHAPTP]R VII. 



RESPIRATORY SYSTEM. 



§219. 



The respiratory organs are absent with only a few of the Cephalophora ; 

 namely : with Sagitta, the Apneusta, and with some of the Pteropoda and 

 Heteropoda.'^' With these, therefore, it may be inferred that the respira- 



* Erdl (De Helicis algirae, &c., loc. cit.) has, in- 

 deed, fiRvwed venous net-works on the digestive 

 apparatus of an Helix (see also its copy in Cams' 

 Erlauterungstafeln, Hf. VI. Tab. II. fig. 5) ; but I 

 regard tliese as of an arterial nature, and this so 

 much the more, since Erdl, in his dissertation, has 

 nowhere shown a direct communication between 

 the arteries and veins. The absence of a caj^illary 

 net-worli and of venous radicles, is quite apparent 

 with Arinn, in which tlie posterior artery forms 

 beautiful ramifications of a white color upon the in- 

 testiue and liver. If the larger branches of this 

 artery are examined, their muscular walls will be 

 distinctly seen to be internally lined with a granu- 

 lated layer composed of carbonate of lime and which 

 gives the color just mentioned. 



If also the smaller l)ranches are examined, their 

 muscular walls will be found to have gradually dis- 

 appeared so that the blood circulates inside of the 

 granular layer only; and this last in its turn will also 

 be found to have disappeared leaving no trace of 

 capillaries or venous radicles. For the details of 

 the arterial system of the Cephalophora, see the 

 Memoires of Kan Ben rrfcn, loc. cit. (I'teropoda) ; 

 Milne Edwards, Ann. d. Sc. Nat. XVIII. 1S24, 

 p. 325, PI. XI. fig. 1 {Carinaria), and Cuvier, 

 Meckel, and Delle Chiaje, loc. cit. ((Jasteropoda). 



5 Although Cuvier in 1803 (Ann. du Mus. d'Hist. 

 Nat. II. p. 299, PI. II. fig. 1, 3) perceived, on the in- 

 •ner surface of the envelop' of the body, the orifices 

 of the venous canals, which as a net-work traverse 

 the fleshy walls of Apli/sia even to the base of the 

 branchiae, and although this was confirmed by 

 Treviranus (Biologic, IV. p. 238) and Delle 

 Chiaje (Memor. &c. I. p. 63), yet it is only lately 

 that the opinion has been recognized tli.at this 

 might be so with all the Cephalophora, for the ob- 

 servation upon Apltjsia remained thus long isolat- 

 ed. Rut now, facts of this kind are so numerous as 

 not to be based u;;en e.\cei)tional observations. It 

 should beunderstoo 1, however, that the absence of 

 capillaries and of \enous radicles, as well as the 

 presence of numerous orifices opening into the ve- 

 nous canals, are the rule with all the Cephalophora 



which have respiratory organs. These orifices may 

 be easily seen, especially by asphyxing species of 

 Limax and Arion, — by which experiment, will be 

 aifpreciated the correctness of Delle Chiaje's figure 

 of Arion which was engraved in 1830 (Memor. loc. 

 cit. Tav. CIX. fig. 16 without text, and Descriz. 

 loc. cit. n. 1811. p. 10, Tav. XXXVII. fig. 16, the 

 same plate with text), with the exception that there 

 are orifices on their ramifications as well as on the 

 two principal canals. Pouchet (loc. cit. p. 19. 

 has named these Orijices absorbants, and his ob- 

 servations were also made on Arion; but Milne 

 Edwards and I'alenciennes (Compt.Rend. loc. cit.) 

 have demonstrated this structure with Aplijsia, 

 Doris, Polycera, Scyllaea, Patella, Chiton, 

 Haliotis, Noturchus,Umbrella, Pleurobranchns. 

 Dolabclla, Bticcinum, Tritonium, Turbo, Am- 

 pvllaria, Onchidiiim, Helix, &c., and therefore 

 with the Nudibranchia, Cyclobranchia, Scutibran- 

 chia, Tectibranchia, Pectinibranchia, and Pulmon- 

 ata. I must here repeat that these venous canals 

 are only lacunae excavated in the muscular 

 walls of the body, and are without proper walls, 

 as Meckel (Syst. d. vergleich. Anat. V. p. 12S) has 

 pretended is the case with those of Aplysia. To be 

 convinced of their wall-less structure it is only nee s- 

 sary to examine microscopically a longitudinally 

 incised Arion . They will be found composed whilly 

 of muscular fibres interlaced in every direction, an.l 

 some of which surround, sphincter-like, the venous 

 orifices, thus showing that those last are not closed 

 liy valves, but by the contraction of these fibres. 

 Souleyet himself could not deny this wall-less struc- 

 ture in the veins of the Gasteropoda, although it is 

 in contradiction with his statements against Phle- 

 benterismus. lie declares (Conipt. Rend. XX. p. 

 81, note 3) " que le systc^me veineux dcs Mollus- 

 ques n'est jias tmijours forme iiar des vaisseux dis- 

 tincts, mais ciu'il, se compose en gran<le partie 

 de ces canaux creuses dans IVjiaisseur ou dans 

 I'interstice des orgaues." See ;iJso below §216, 

 note 1. 



I Respiratory organs appear to bo wholly ab- 

 sent in Sa^^itta, and Phyllirrhoii. 



