246 



THE CEPHALOPHORA. 



^21T. 



§ 217. 



The Heart is wanting in only a few genera of the Cephalophora.''* Almost 

 always it has a pericardium/-' and is divided into a simple, very muscular 

 ventricle, and a thin-walled auricle which is equally simple, rarely double.® 



The arterial blood passes from the respiratory organs into the auricle, 

 thence into the ventricle, from which it is forced through a very short aorta 

 over the body. These two chambers of the heart are usually pyriform, and 

 are joined together at their large extremity by a constriction in which is 

 sometimes situated a valve, which prevents the return of the blood into the 

 auricle. ^■'^ 



The position of the heart usually depends upon that of the respiratory 

 organs. It is generally situated at the base of the branchiae, or in the 

 bottom of the pulmonary cavity. It is most often found, therefore, upon 

 the right side of the body.*^^ 



Von den iiusser. Lebensbeding. d. weiss-und 

 Kaltblutisen Tliiere. p. 72 ; Ehrenberg, Uner- 

 kaniite Struct, loc. cit. Tab. VI. fig. I. 1, II. 1 

 {Avion and Paludina) ; and Erdl, De Helicis 

 algirae vasis sanguiferis. Diss. Monach. 1840, p. 

 10. 



With Planorbis, the blood is red. With the 

 Cephalophora in general, there is only a very 

 small quantity of fibrine, at least there is only a 

 trace in the blood of He/ix ; it forms a kind of a 

 web, scarcely visible, uniting the globules into mass- 

 es and rows. The nuclei of these blood-globules 

 become very distinct by the addition of acetic acid.* 



1 Forbes (Instit. 1843, p. 358), and Darwin (Ann. 

 of Nat. Hist. XIII. p. 3), have been unable to find 

 a heart with Sagitta ; although D''Orbigny (Voy. 

 dans I'Amer. mer., or Isis. 1839, p. 501) affirms 

 that he has seen the movements of this organ in 

 this enigmatical animal, and Darwin (loc. cit. 

 p. 6) has perceived a pulsating organ at the 

 anterior extremity of the embi'yos. The heart 

 is wanting, according to Quatrefages (loc. cit. 

 I.), in Zephyrina, Actaeon, and Amphorina ; 

 and according to Kiilliker, in Flabellina, Rho- 

 dope, and Lissosoma. However, Souleye.t 

 (Comp. Rend. XX. 1845, p. 73) contradicts, very pos- 

 itively, the assertions of Quatrefages, and assigns 

 a heart to all the Apneusta. The difficulties in the 

 study of these animals, from theu- non-transparency, 

 are undoul)tedly the cause of many of these contra- 

 dictory statements. One should not, also, conclude 

 as to the organization of the adults from the develop- 

 ment of the embryos ; for it is very singular that 

 the embryos of Actaeon are completely developed 

 without a heart (Fogt, Comp. Rend. XXI. No. 14, 

 XXII. No. 9, or Froriep''s neue Not. No. 795, 



* [ § 216, note 2.] Leydig (loc. cit.) describes 

 the bloc d of Paludina as containing two forms of 

 corpuscles ; one, round, which became granular 

 nucleated cells after the action of acetic acid ; 

 the other provided on one side with processes 

 which disappeared upon the action of acid ; see 

 loc. cit. p. 170, Taf. XII. fig. 47, 48. In this con- 

 nection, see also for the blood-cori)Uscles of the 

 Gasteropoda (Buccinum magnum) and their de- 

 velopment, fVharton Jones, Phiios. Trans. 1846, 

 Part II. p. 96, PI. II. fig. 1-7, of the Gasteropoda 

 division. Jones also mentions the stellate form of 

 the corpuscle (fig. 4). It would appear to me that 

 this piiculiarity la, after all, only a creuulation due 



and 820), while with the other Gasteropoda the 

 heart appears very early in the embryonic de- 

 velopment. Acconling to Nordmann (loc. cit. p. 

 93), the embryos of Tergipes, which has a heart, 

 are developed as those of Actaeon, thus showing 

 that the absence of this organ in these last is only 

 a delay of its appearance. 



Wilms (loc. cit. p. 11) has been also equally 

 unable to find a heart with Sagitta. 



2 The pericardium is apparently wanting with 

 the Apneusta. 



3 Chiton, Haliotis, Fissurella, and Emargi- 

 nula have two lateral auricles ; the last three of 

 these Scutibranchia resemble moreover the La- 

 mellibranchia in their heart being traversed by 

 the rectum ; see Cuvicf, loc. cit., and Meckel, 

 Syst. d. vergleich. Anat. \. p. 115. 



4 See Cuvier, loc. cit. PI. I. fig. 2-4, II. fig. 1 ; 

 Cams, Erlauterungstafeln lift. VI. Taf. II. fig. 6 

 {Helix) ; and Fan Beneden, Exerc. zoot. loc. cit. 

 PI. III. fig. 11 (Hyalea). 



Nordmann Qoc. cit. p. 26, Tab. III. fig. 4) 

 found with Tergipes, the auriculo-ventricular val- 

 vular apparatus replaced by a yery movable valve 

 situated between the ventricle and the bulb of the 

 aorta. With Umax, and Arion, the valves are 

 wholly wanting (Treviranus, Beobacht. aus d. 

 zoot. u. Phys. p. 40). 



5 The heart is situated on the right side of the 

 back, with most of the Tectibranchiii, with the 

 dextral Pectinibranchae, and Pulmonata, and with 

 all the Limacina ; while it is on the opposite 

 side with Ancylus, Haliotis, and all the sinistral 

 Gasteropoda. That of Carinaria, Clio, Hyalea, 

 and Cleodora, is upon the dorsal median line, a 

 little to the left, t 



to an exosmotic passage of the cell-contents — leav- 

 ing the cell-membrane thus deeply wrinkled, as 

 may often be observed also with the blood of verte- 

 brates. — Ed. 



t [ § 217, note 5.] With Firola, and Atlanta, 

 the heart is situated near the posterior extremity 

 of the body ; its auricle and ventricle are com- 

 posed of interlaced, striated muscular fibres ; both 

 the auriculo-ventricular and the aorto-ventricular 

 orifices are valvular ; see Huxley, Ann. d. Sc. Nat. 

 XIV. 1850, p. 193. 



See also, for the heart its positions and connec- 

 tions, with the Lymnaeacea, De St. Simon, Jour 

 de Conchol. 1852, II. p. 113. — Ed. 



