248 
THE CEPHALOPHORA. 
§ 219. 
opens into the veins, but gradually disappear,® so that it is probable that 
the blood is effused from 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 in the muscular substance of the envelope of the 
body. 
CHAPTER VII. 
RESPIRATORY SYSTEM. 
§ 219. 
The respiratory organs are absent.with only a few of the Cephalophora; 
mamely : with Sagitta, the Apneusta, and with some of the Pteropoda and 
Heteropoda.™ 
4 Erdl (De Helicis algirae, &c., loc. cit.) has, in- 
deed, figured venous net-works on the digestive 
apparatus of an Helix (see also its copy in Carus’ 
Erliuterungstafeln, Hf. VI. Tab. II. fig. 5); butI 
regard these as of an arterial nature, and this so 
much the more, since rd, in his dissertation, has 
nowhere shown a direct communication between 
the arteries and veins. The absence of a capillary 
net-work and of venous radicles, is quite apparent 
with Arion, in which the posterior artery forms 
‘beautiful ramifications of a white color upon the in- 
testine 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- 
dated layer composed of carbonate of lime and which 
gives the color just mentioned. 
If also the smaller branches are examined, their 
muscular walls will be found to have gradually dis- 
appeared so that the blood circulates inside of the 
gyanular 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 
Mémoires of Van Beneden, loc. cit. (Pteropoda) ; 
Milne Edwards, Ann. d. 8c. Nat. XVIII. 1824, 
p. 325, Pl. XI. fig. 1 (Carinaria), and Cuvier, 
Meckel, and Delle Chiaje, loc. cit. (Gasteropoda). 
5 Although Cuvier in 1803 (Ann. du Mus. d’Hist. 
Nat. II. p. 299, Pl. II. fig. 1,3) perceived, on the in- 
ner surface of the envelope of the body, the orifices 
of the venous canals, which as a net-work traverse 
the fleshy walls of Aplysia even to the base of the 
branchiae, and although this was confirmed by 
Treviranus (Biologie, IV. p. 238) and Delle 
Chiaje (Memor. &c. I. p. 63), yet it is only lately 
that the opinion has been recognized that this 
aight be so with all the Cephalophora, for the ob- 
servation upon Aplysia remained thus long isolat- 
ed. But now, facts of this kind are so numerous as 
not to be based upon exceptional observations. It 
should be understood, however, that the absence of 
capillaries and of venous radicles, as well as the 
presence of numerous orifices opening into the ve- 
nous canals, are the rule with all the Cephalophora 
‘are only lacunae excavated 
With these, therefore, it may be inferred that the respira- 
which have respiratory organs. These orifices may 
be easily seen, especially by asphyxing species of 
Limaz and Arion, — by which experiment, will be 
appreciated 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. II. 1841, p. 10, Tav. XX XVII. 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 Orifices absorbants, and his ob- 
servations were: also made on Arion; but Milne 
Edwards and Valenciennes (Compt.Rend. loc. cit.) 
have demonstrated this structure with Aplysia, 
Doris, Polycera, Scyllaea, Patella, Chiton, 
Haliotis, Notarchus,Umbrella, Pleurobranchus, 
Dolabella, Bucci , Tritonium, Turbo, Am- 
pullaria, Onchidium, Helix, &c., and_ therefore 
with the Nudibranchia, Cyclobranchia, Scutibran- 
‘chia, Tectibranchia, Pectinibranchia, and Pulmon- 
ata. I must here repeat that these venous canals 
i in the muscular 
walls of the body, and are without proper walls, 
as Meckel (Syst. d. vergleich. Anat. V. p. 128) has 
pretended is the case with those of Aplysia. Tobe 
convinced of their wall-less structure it is only neces- 
sary to examine microscopically a longitudinally 
incised Arion. They will be found composed wholly 
of muscular fibres interlaced in every direction, and 
some of which surround, sphincter-like, the venous 
orifices, thus showing that these last are not closed 
by 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 contradictién with his statements against Phle- 
benterismus. He declares (Compt. Rend. XX. p. 
81, note 3) “que le systéme veineux des Mollus- 
ques n’est pas toujours formé par des vaisseux dis- 
tincts, mais qu’il, se compose en grande partie 
de ces canaux creusés dans l’épaisseur ou dans 
Vinterstice des organes.” See also below § 216, 
note 1. 2 
1 Respiratory organs appear to be wholly ab- 
sent in Sagitta, and Phyllirrhoé. 
