^218. 



THE CEPHÄLOPHORA. 



247 



It lies upon the median line, and its ventricle and aorta are directed for- 

 wards, in those genera whose respiratory organs are symmetrical, or wholly 

 wanting. <•"'> With many other Cephalophora, they have also the same di- 

 rection, without, however, being situated on the median line ; but in the 

 turbinated genera, the apex of the ventricle and the aorta are directed back- 

 wards. 



§ 218. 



The vascular system of the Cephalophora consists almost solely of arte- 

 ries with their branches, of large venous canals receiving the blood from 

 the cavity of the body, and of the lacunae in the parenchyma which return 

 it to the respiratory organs. 



With Sagiita,'-^^ and some Apneusta® there are no traces of blood-ves- 

 sels ; and, as with the Nematodes, the nutritive liquid transudes directly 

 through the intestinal canal into the cavity of the body. 



In another series of the Apneusta, there are rudiments of arteries and 

 veins, in the form of a short aorta, which passes in front from the ventricle, 

 and has a bifurcated extremity, — and two vena cava even shorter, which 

 open each side of the posterior end of the auricle. *^^ 



With the other Ce] ' ^ophora, the aorta divides, after a short course, into 

 two principal arteries, i^^ anterior of which passes through the oesopha- 

 geal ring, and, sending branches to the cephalic organs, finally ramifies in 

 the fleshy walls of the body ; but the other, posterior, ramifies over the 

 organs in the intestinal sac. These ramifications, which sometimes form a 

 beautiful vascular net-work, never pass into a capillary system which 



6 Tlie heart is situated on the median line of the 

 bacli in Dentalium, Tritonia, Scyl/aea, Thetis, 

 Phyllidia, Fissurel/a, and Eniar^inula ; upon 

 the posterior part of the body, with Doris, and 

 Chiton, as is also the case with Onchidium which 

 is remarkable in other respects. It is singular 

 that with Patella, whose respiratory apparatus is 

 Bymmetrically disposed, the position of the heart is 

 in front and on the right side ; see Meckel, Syst. 

 d. vergleich. Anat. A', p. 119, and Arch, für Anat. 

 u. Phys. 1826, p. 19. Several of the Apneusta 

 have the heart on the dorsal median line, as for 

 examples, Ter^ipes {Nordmann, loc. cit. p. 24, 

 Tab. II. T., Tab. III. fig. 4), Eolidina {Quatre- 

 fnges, loc. cit. XIX. p. 288, PI. XI. fig. 3), Aeolis 

 {Hancock and Embleton, loc. cit. PI. V. fig. 16), 

 and Actaeon {Allman, loc. cit. p. 149, PI. V. 

 fig. 4). 



1 Krohn, loc. cit. p. 8. 



Notwithstanding» the absence of a heart and a 

 vascular system with Sagitta, Wilms (loc. cit. p. 

 12), has found in the visceral cavity of these ani- 

 mals regular blood-currents, due, probably, to cil- 

 iated organs. 



2 Flahellina, Lissosoma, and Rhodope, ac- 

 cording to Kölliker ; Zephyrina, and Amphorina, 

 according to Quatrefages. 



3 Such a rudimentary vascular system situated 

 in the anterior part of the back, has been seen by 

 Nordmann (loc. cit. p. 24), with Tergipes, by 



Quatrefages (loc. cit. p. 288), with Eolidina, and 

 by Van Beyieden (Instit. No. 627, or Froriep's 

 neue Not. No. V97, p. 68), with Aeolis. 



Allman, judging from one of his figures (loc. 

 cit. PI. V. fig. 4, c), hasfoundit also with ^cfaeo«. 

 Nordmann has observed, that in spite of this im- 

 perfection of the blood-vessels, the blood effused 

 into the cavity of the body circulates regularly, so 

 that with Tergipes, the whole body, including the 

 appendages, is traversed by arterial and venous 

 currents which can be traced even to the two 

 venae cavae which arise from open mouths. This 

 circulation is quite like that of insects ; except that 

 here, the blood of the Apneusta continues a longer 

 course in the arteries, for Nordmann, with Ter- 

 gipes, and Quatrefages, with Eolidina, have 

 been able to trace on each side of tlie body an an- 

 terior and posterior branch of the aorta. Quatre- 

 fages, however, commits an error at the outset 

 concerning this simple circulation of the Apneusta, 

 in declaring that with these Gasteropoda the rami- 

 fied intestinal canal serves also the function of a 

 vascular system ; this has induced him to give the 

 name Phlebenterata to an entire group of these 

 animals. In the controversy between him and 

 Souleyet on this subject (Comp. Rend. XIX. XX.), 

 and which threatens to be interminable, this last 

 has gone too far in asserting that, not only with the 

 Apneusta, but even with all the G asteropoda, there 

 is a completely-closed vascular system.* 



* f § 218, note 3.] See, for detailed remarks 

 agamst the doctrine of Plilebenterism with the Eoli- 

 didae, Hancock and Embleton (loc. cit. 1849). 

 They have shown here the existence of a pretty 



highly-developed vascular system commencing in a 

 well-formed heart which consists of a ventricle and 

 an auricle, and enclosed in a pericardium. — Ed. 



