§ 218. THE CEPHALOPHORA. 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 Sagitta,” 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 Cephalophora, the aorta divides, after a: short course, into 
two principal arteries, the anterior of which passes through the cesopha- 
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. 
beautiful vascular net-work, never 
6 The heart is situated on the median line of the 
back in Dentalium, Tritonia, Scyliaea, Thetis, 
Phyllidia, Fissurella, and Emarginula; upon 
the posterior part of the body, with Dorzs, 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 
symmetrically disposed; the position of the heart is 
in front and on the right side ; see Meckel, Syst. 
d. vergleich. Anat. V. p. 119, and Arch. fiir Anat. 
u. Phys. 1826, p.19. Several of the Apneusta 
have the heart on the dorsal median line, as for 
examples, Tergipes (Nordmann, loc. cit. p. 24, 
Tab, II. T., Tab, IIL. fig. 4), Eolidina (Quatre- 
Sages, loc. cit. XIX. p. 288, Pl. XI. fig. 3), Aeolis 
(Hancock and Embleton, loc. cit. Pl. V. fig. 16), 
ou Actacon (Aliman, loc. cit. p. 149, Pl. V. 
g. 4). 
1 Krohn, loc. cit. p. 8. ° 
Notwithstandinge 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 Flabellina, Lissosoma, and Rhodope, ac- 
cording to Kélliker ; Zephyrina, and Amphorina, 
according to Quatrefages. 
8 Such a rudimentary v lar system 
in the anterior part of the back, has been seen by 
Nordmann (loc. cit. p. 24), with Tergipes, by 
*[§ 218, note 3.) See, for detailed remarks 
against the doctrine of Phlebenterism with the Eoli- 
didae, Hancock and Embleton (loc. cit. 1849). 
They have shown here the existence of a pretty 
These ramifications, which sometimes form a 
pass into a capillary system which 
Quatrefages (loc. cit. p. 288), with Eolidina, and 
by Van Beneden (Instit. No. 627, or Froriep’s 
neue Not. No. 797, p. 68), with Aeolis. 
Allman, judging from one of his figures (loc. 
cit. Pl. V. fig. 4, c.), has found it also with Actaeon. 
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 T'ergipes, 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 ou each side of the body an an- 
terior and posterior branch of the aorta. Quatre- 
Jages, 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 Gasteropoda, there 
is a completely-closed vascular system.* 
highly-developed. lar system ina 
well-formed heart which consists of a ventricle and 
an auricle, and enclosed in a pericardium. — Ep. 
