212 THE ACEPHALA. 
$ 195. 
§ 195. 
It now remains to speak of a particular system of canals traversing in 
all directions the body of the Lamellibranchia, which as yet has been 
called the aquiferous system, because it is supposed to serve for an internal 
respiration like that of the tracheae of insects.” But, in the first place, 
the existence itself of such a system has been denied, although there are 
certain facts in its favor. 
When one of these animals is suddenly taken from the water, numerous. 
fine jets of water are seen to pass from these organs while the animal is 
withdrawing its foot and the borders of the mantle within the shell. From 
this fact it is evident that these orifices connect with aqueous reservoirs. 
But these openings are very small and probably are closely contracted, for 
they cannot be discovered either before or after the jetting out of the wa- 
ter.” Orifices of this kind have as yet been found in a few species only ; 
such are those in the extremity of the foot of Solen,® and that singular 
tube found above the pedunculate anus of Pinna. 
The aquiferous canals themselves are not very apparent, being seen only 
after injection. This last is easily performed by blowing through a smal} 
tube inserted under the skin. There will then be seena very beautiful net- 
work of canals, which, nearly all of the same size, are spread out under 
almost the whole skin and enter the interior of the body by larger canals. 
These canals appear to be without walls, and have, in general, the aspect of 
simple lacunae traversing the parenchyma of different parts of the body. 
By some naturalists, this net-work of canals is regarded as a system of 
lacunae circulating the blood ;® but when they are inflated, another net- 
Janus, Isis, 1819; T'reviranus, Beobacht. &c. p. 
44, and the beautiful figures of Poli, loc. cit.* 
1 Baer was the first to call the attention to this 
aquiferous system with the Naiades (Froriep’s neue 
Not. No. 265, 1826, p. 5) after an analogous one 
had been pointed out with the Gasteropoda by 
Delle Chiaje. Poli, it is true, had recognized it 
before this, but he had taken them partly for tra- 
cheae aad partly for lymph or blood-vessels. 
2 Meckel (Syst. d. vergleich. Anat. VI. p, 64) 
went certainly too far when he affirmed that these 
orifices are only accidental fissures. I have been 
unable to find the orifices, which, according to Poli 
(oc. cit. Introductio, p. 42, 52), are upon the summit 
of the cirri of the mantle and lead into a tracheal 
system. 
. 3 Orifices of this kind have been described and 
figured by Delle Chiaje with Solen siliqua, as 
Fort aquiferi (Descriz. &c. ILI. p. 60, Tav. XC. fig. 
11). These pores communicate probably with an 
aquiferous system which Treviranus has seen in 
the foot of Solen ensis (Die Erschein. u. Gesetze 
*[§ 194, note 20.) For full details on the branch- 
jal vessels of Teredo, and beautifully illustrated, 
see Deshayes, loc. cit. p. 69, Pl. VII. and Quatre- 
Sages, Mémoire, loc. cit. p. 57, Pl. II. See also 
Williams, On the Structure of the Branchiae and 
Mechanism of Breathing in the Pholades and other 
Lamellibranchiate Mollusks, in the Report of the 
Brit, Assoc. for the Advancem. of Sc. for 1851, p. 82, 
His firat four conclusions are ; 
“1, That the blood of all Jamellibranchiate mol- 
lusca is richly corpusculated. 
des organisch. Lebens. I. p. 276). The orifice 
which Garner has figured upon the middle of the 
foot of Psammobia and Cardium, and to which 
he has given the name of Porus pedalis, belongs 
undoubtedly to this system ; see Trans. of the Zool. 
Soc. II. Pl. XVIII. fig. 2, 13, f. 
4 Ihave easily inflated the reticulated aquiferous 
canals of this animal by this tube, which, in Pinna 
nobilis, sometimes protrudes far beyond the bor- 
ders of the mantle, and which Podz (loc. cit. II. 
p. 241, Tab. XXXVI. fig. 3, N. fig. 7, Z. and Tab. 
XXXVIL fig. 1,8.) has figured as a T'rachea. 
5 See above §192, note 11. The vascular net~ 
work which Polz (loc. cit. I. p. 8, Tab. IX.) has in- 
jected with mercury in the mantle of a Unio, and 
which he regarded as a lymphatic system, belongs. 
probably to the aquiferous system. The same in- 
terpretation ought perhaps to be put upon a san- 
guineous net-work which he has figured in the man- 
tle of a Pinna (loc. cit. Tab. XX XVIII.). Delle Chi-~ 
aje (Descriz. &c. III. Tav, LXXV. fig. 6, Tav. 
LXXVL. fig. 3, 6,and XC. fig. 1, 2, LKX XIX. fig. 
“2, That the branchiae in all species are com- 
posed of straight parallel vessels returning upon 
themeelves. 
“©3, That the heart is systemic and not branchial. 
“4, That the parallel vessels of the gills are 
provided with vibratile cilia disposed in a linear se- 
ries on either side of the branchial vessel, causing 
currents, which set in the direction of the current 
of the blood in the vessels.” — Ep. 
