^216. 



THE CEPHALOPHOBA, 



245 



2. With the other Cephalophora, the liver is wholly isolated, nearly always 

 asymmetrical/'^' and often divided into several lobes of a yellowish-brown 

 or brownish-green color; often, also, it wholly envelops the intestinal con- 

 volutions. The biliary canals, which arise from the hepatic lobes, form 

 usually, two, three, or more excretory ducts, which empty the bile into the 

 «tomach or intestine, rarely into the oesophagus/* 



CHAPTER VI. 



CIRCULATORY SYSTEM. 



§216. 



For a long time it was erroneously supposed that the circulatory system 

 of the Cephalophora was completely closed. But the heart or central portion 

 of this system, is developed in an inverse ratio to the imperfect peripheric 

 part which is without a capillary net-work. This incompleteness is often 

 so great that, in many genera, the arteries are wanting and the veins more 

 or less wholly absent. The circulation is, therefore, extravascular for a 

 longer or shorter course, and passes into cavities {Lacunae) situated in 

 the parenchyma of the body.^^' 



The blood is colorless, often opalescent, and always very poor in corpus- 

 cles. These last are also colorless and consist of smooth cells, with a 

 granular, indistinct nucleus.*-' 



7 With Dentalium, there are two symmetrical 

 livers, one ou each side of the intestinal canal ; see 

 Deshayes, loc. cit. PI. XV. fig. 11, or Isis. Taf. VI. 

 fig. 15, m. m. With Diphyltidia, also, there are 

 two livers, one on each side of the stomach into 

 which they open by several transverse excretory 

 canals ; see Mec/cefs Arch. 1826, p. 15, Taf. I. 

 fig. 11. 



** For the external form of the liver, consult Cu- 

 I'ier, loc. cit. The hepatic ducts open, near the 

 pyloric orifice, with Limax, Helix, Testacella, 

 Doridiuin, and Dentalium ; into the intestine, with 

 Ilaliotis, Vermetus, Pleurobranchus, Diphylli- 

 din, Doris, Planorbis, and Lymnaeus ; into the 

 third stomach, with Aplynia, Dolabella, and Notar- 

 <;A!<s,- while with Onchidium, two of the ducts open 

 into the cesophagus, and the third into the first 

 stomach.* 



1 The tenacity with which the opinion was enter- 

 tained that there is a completely-closed vascular 

 system with the Mollusca, is shown in the fact that 

 Cuvier (Kiigne auim. I. p. 50), after having seen, 



* [ § 215, note 8.] For the details of the hepatic 

 structure with the Nudibranchia, see Alder and 

 Hancock, loc. cit. Part II. PI. II. flg. 2, e. hh., 

 and fig. 3 (Dendronotus) ; Part III. PI. VIII. fig. 

 9 (Aeolis); Part IV. PI. V. fig. 1, g. g. g. {Scyl- 

 iaea), and fig. 8, g g. {Eumenis) ; Part V. PI. I. 

 fig. 2, d. d., and PI II. fig. 1, f. {Doris). 



21# 



with Aplysia, the veins communicate distinctly 

 with the cavity of the Ijody by special orifices, still 

 persisted in the old view, — regarding this as an 

 exception ; see Mem. loc. cit. p. 13. It is only 

 latterly that the circulation of the blood through 

 the lacunae and interstices of the body, has been 

 shown to be the rule, by Pouchet (Recherches loc. 

 cit. p. 13), Milne Edwards and Falenciennes 

 (Compt. rend. XX. 1845, p. 261, 750, or Froriep^s 

 neue Not. XXXIV. p. 81, 257). 



Milne Edwards, in his memoir already cited 

 upon the circulation of Patella, Haliotis, Helix, 

 Aplysia, Thetis, and Triton, has abundantly 

 shown that the vascular system of the Ceijhalo- 

 phora is also incomplete, and that the aorta termi- 

 nates in a large lacunal sinus containing the brain, 

 the salivary glands, the oesophagus with its mus- 

 cles, and the retracted tongue, and which forms also 

 a part of the visceral cavity ; see Ann. d. Sc. Nat. 

 VIII. 1847, p. 37, PI. I.-III., or SclUeiden and 

 Froriep\f Not. V. p. 1, fig. 1 — 4. 



2 For the blood of the Gasteropoda, see Cams, 



For the liver of Chiton, see Middendorf (Bei- 

 trage zur einen Malacozoologia rossica, St. Peters- 

 burg, 1847, p. 63, Taf. V. fig. 2, 1.). Its ducts open 

 into the alimentary canal near the stomach. — Ed. 



