252 THE CEPHALOPHORA. § 228. 
for, upon the back and directly behind the heart, there is a reservoir 
filled with water, from which ramifying canals pass off in all directions.® 
The older observations upon these aquiferous canals of the Pteropoda, 
Heteropoda, and Gasteropoda, have been but indifferently increased by 
more recent labors. With these Cephalophora, the substance of the 
envelope of the body is permeated by a beautiful net-work of wall-less 
canals, which are filled wita water, it is supposed, through several orifices 
upon the surface of the body.” It is, nevertheless, far from being settled 
that these canals belong to an aquiferous system, for the existence of their 
external orifices is doubtful, and it may be urged that they are only a con- 
tinuation of the venous system. At all events, this question demands 
further researches based upon facts observed with the Acephala and 
Cephalophora. 
CHAPTER VIII. 
ORGANS OF SECRETION, 
I. Urinary Organs. 
§ 223. 
With most of the Cephalophora, the Urinary apparatus consists of an un- 
even, lamellate gland, which is usually situated near the branchial or princi- 
1 According to Souleyet (Compt. Rend. XIX. p. 
360, XX. p. 93), there is, with Actaeon, an aquif- 
erous system, arising from a reservoir of water 
situated behind the heart, and which he has called 
Poche pulmonaire, which is spread through the 
whole of the body. Vogt, as he has written me, 
has distinctly seen this system with a canal open- 
ing on the right side behind the anus. Allman 
(loc. cit. p. 148, Pl. V. fig. 4, a. a. b.) has also 
observed it in the same species, but he took it for a 
blood system. The canal, which, with Venilia, 
opens at the posterior part of the back, and which 
has been taken by Alder and Hancock (loc. cit. 
XIII. Pl. IL. fig. 1, 7, b.) for the rectum with its 
anus, belongs also, perhaps, to an aquiferous sys- 
tem, as well as the orifice figured by Dedle Chiaje 
(Descriz. loc. cit. Tay. LXXXVIII. fig. 2, d.) in 
the same region, wtih Aeolis cristata (Venilia 2). 
2 Delle Chiaje is as yet the only naturalist who 
has published quite detailed researches upon the 
aquiferous canals of the Cephalophora indicated in ~ 
the text. In an earlier work, he has described 
them with Doris, Thetis, Aplysia, Pleuro- 
branchus, Pleurobranchaea, Bulla, Doridium, 
Diphyllidia, Turbo, Trochus, Nerita, Conus, 
Cypraea, Voluta, Buccinum, Murex, Ceri- 
thium, Rostellaria, Haliotis, and Patella, as 
canals which traverse the foot, opening, for the 
most part, on its borders by numerous orifices (see 
his Descrizione diun nuovo apparato di canali ac- 
quoai scoperto negli auimali invertebrati marini, 
in his Memor. &c. II. p. 259, Tav. XVII. fig. 10- 
15). Since then, he has described this system, 
which, he says, is wanting with the aquatic Pulmo- 
uitd, a3 a beautiful, subcutaneous net-work. He 
has named it Apparato idro-pneumatico or Sis- 
tema linfatico-venoso ; see his Descriz. I. p. 88, 
&e., Tav, XXXII. XXXIV. XL. &. (Cymbulia, 
Hyalea, Carinaria, Pterotrachea, Doris, Tri- 
tonia, Thetis, Pleurobranchaea, Diphyllidia, 
Doridium, Gasteropteron, Aplysia, Bulla, Si- 
garetus, and Janthina). With Cymbulia, and 
Gasteropteron, this aquiferous canal communi- 
cates with a large sinus from which passes off a 
long afferent canal which projects from the surface 
of the body (see Delle Chiaje, Descriz. loc. cit. Tay. 
XXXII. fig. 1, 2, g. LV. fig. 2, b. f. 4. ¢. a). 
3 Meckel (Syst. d. vergleich. Anat. VI. p. 72) 
positively denies the existence of an aquiferous 
system and its external orifices. But he maintains 
that the marine Cephalophora can absorb and re- 
ject simply by their skin, considerable quantities 
of water, without the need of special orifices. 
Milne Edwards (Compt. Rend. XX. p. 271, 
or Froriep’s neue Not. No. 733, p. 98) declares 
that this apparatus, such as described by Delle 
Chiaje, belongs to the venous system. He also 
denies the existence of extérnal orifices, explain- 
ing the ingress and egress of water which has 
been observed with these animals, as due to endos- 
mose and exosmose. Van Beneden, also (Ann. d. 
Sc. Nat. IV. 1835, p. 250), says that he is convinced 
that with Aplysia the so-called aquiferous canals 
are only a dependence of the venous system. On 
the other hand, he is inclined to admit that, with 
Aplysia, and Carinaria, &c., there are small ori- 
fices by means of which these animals can mix 
water with their blood (Compt. Rend. XX. p. 520, 
apd l'Institut. No. 627, or Froriep’s neue Not. No 
727, p. 4, and No. 797, p. 65). 
