$ 196. THE ACEPHALA. 213 
work of mach suulier canals is seen expanded between and above them, 
and which can be ouly the blood-canals that were already visible before 
inflation. But the existence with these animals of a double system of 
dJacunae having this interpretation, is attended with many difficulties. For 
then it must be admitted that one of these systems contains only water, and 
the other blood; and it is difficult to understand how two kinds of wall-less 
canals can traverse the body without passing into each other. But then, on 
the other hand, if the aquiferous canals are regarded as veins, and the other 
canals as arteries, how can this be reconciled with the fact that, in this case, 
the blood system would open externally and the blood escape through the 
natural orifices, while the water would be mixed with it from passing into 
the hody? At all events, this portion of the organization of these ani- 
mals still requires a more thorough investigation. 
CHAPTER VIII. 
ORGANS OF SECRETION. 
§ 196. 
The relations of the mantle to the 
the byssus-forming organ, have already been spoken of.” 
11) has given very beautiful figures of the aquifer=- 
‘ous system of the mantle and foot of Pecten, Pin= 
na, Solen and Mactra, but has regarded it asa 
Rete lymphatico-vasculosum. Milne Edwards 
(Compt. Rend. XX. p. 271, or Ann. d. Sc. Nat. III. 
1845, p. 300, or Froriep’s neue Not. No. 733, p. 
99), who has seen these canals in Pinna, Mactra, 
Ostrea, &c., regarded them simply as a system of 
lacunae common to all the Acephala. 
61 have seen it thus, at least with Unio, and 
Anodonta, 
7 Delle Chiaje (Descriz. &c. III. p. 53) thinks 
that, with the Lamellibr ia, the sangui 
system opens externally through special orifices. 
* [§ 196, note 1.] The means by which the 
Teredina penetrate the woody or stony substances 
in which they live, have received some investigg- 
tion of late, and I refer here to the subject from its 
alleged anatomical relations. 
According to Hancock (Proceed. Brit. Assoc. 
for the Advancem. of Sc. 1848, or Ann. of Nat. 
Hist. 1848, II. p. 225, Pl. VIII. or Silliman’s 
Amer. Jour. of Sc. 1849, VII. p. 288), “On a mi- 
nute examination of the surface of the foot of T'e- 
redo Norvegica it is found under the microscope 
to be crowded with minute brilliant points which, 
on being compressed, consist of comparatively 
large crystalline bodies imbedded within them. 
These crystals are numerous and of various sizes 
and shapes, chiefly five and six sided, but not by 
any means regularly so. They all agree in having 
one or more elevated points near the centre. These 
shell-substance and 
It now only 
secretion of the 
1 See above §§ 174,179. According to Deshaycs, 
Teredo has, at the anterior extremity of the body, 
a gland concealed between the valves and which 
communicates with the mouth of the animal. Its 
product would serve to dissolve the wood in which 
this animal bores. This glandular apparatus 
which, according to Deshayes exists also with 
other Teredina which live in calcareous matters, 
demands a further examination ; see Comp. Rend. 
XXII. p. 38, 300, or Froriep’s neue Not. XXXVI. 
p. 824, XX XVIII. p. 103.* 
bodies are highly refractive, and are for the most 
part pretty regularly distributed over the whole con- 
vex surface of the foot, but are occasionally congre- 
gated in masses.” This author thinks that this, as 
also all other boring Mollusks, excavate by means 
of these parts which rasp down the substance to be 
removed. See as corroborative of these views, Clark 
Ann. Nat. Hist. 1850, V. p. 6. But naturalists 
are not agreed on this point, and however it may 
be with Z'eredo, yet with Pholas, other observers 
have failed to find these rasping particles in ques- 
tion ; see areport on the discussion of Hancock’s 
paper in the Athenaeum No. 1086 ; also Quatre- 
Jfages, Mémoire sur le Genre Taret, Ann. d. Sc. 
Nat. 1849, XI. p. 338, and History of British Mol- 
lusca by Forbes and Hanley, p. 105. 
After all, it would seem that it is most probable 
that this process is effected by the action of cilia 
