CONCHIFERA. 390 
its crypt by adyssus. These shell fish have been supposed to 
dissolye the ruck by chemical means (Deshayes), or else to 
wear it away with the thickened anterior margins of the 
mantle.. (Hancock.)* 
The holes of the “ithodomi often serve to shelter other animals 
after the death of the rightful owners; species of Modiola, Arca, 
Venerupis, and Ooralliophaga, both recent and fossil, have been 
found in such situations, and mistaken for the real miners.+ 
The boring shell-fish have been called ‘‘ stone-eaters ” 
(lithophagi) and ‘‘ wood-eaters” (xylophagi), and some of them 
at least are obliged to swallow the material produced by 
their operations, although they may derive no sustenance from 
it. The ship-worm is often filled with pulpy, impalpable 
sawdust, of the colour of the timber in which it worked. 
(Hancock.) No shell-fish deepens or enlarges its burrow after 
attaining the full growth usual to its species (p. 35). 
The bivalves live by filtering water through their gills.} 
Whatever particles the current brings, whether organic or 
Inorganic, animal or vegetable, are collected on the surface 
of the breathing-organ and conveyed to the mouth. In this 
manner they help to remove the impurities of turbid water.§ 
The mechanism by which this is effected may be most conve- 
* All attempts to detect the presence of an acid secretion have hitherto failed, as 
might be expected; for the hypothesis of an acid solvent supposes only a very feeble 
but continuous action, such as in nature always works out the greatest results in the 
end. See Liebig’s Organic Chemistry, and Dumas and Boussingault on the ‘Balance 
of Organic Nature.”  Intimately connected with this question are several other 
phenomena; the removal of portions of the interior of univalves, by the animal 
iiself, as in the genera Conus, Auricula, and Nerita (Fig. 24, p. 32); the perfuration of 
shells by the tongues of the carnivorous gasteropods, and the formation of holes in 
wood and limestone by limpets. Some facts in surgery also illustrate this subject, 
(1) dead bone is removed when granulations grow into contact with it: (2) if a hole is 
bored in a bone, and an ivory peg driven into it, and covered up, so much of the peg as 
is embedded in the bone will be removed. (Paget.) The “absorption” of the fangs 
of milk-teeth, previous to shedding, is well known. In these cases the removal of the 
bone earth is effected without the development of an acid, or other disturbance of the 
neutral condition of the circulating fluid. 
} Fossil univalves (trochi) occupying the burrows of a pholas, were discovered by 
Mr. Bensted in the Kentish-rag of Maidstone. See Mantell’s Medals of Creation. 
M. Buvignier has found several species of Arca fossilised in the burrows cf 
lithodomi. 
f It seems scarcely necessary to remark that the bivalves do not feed upon prey 
caught between their valves. Microscopists are well aware that sediment taken from 
the alimentary canal of bivalve shellfish contains the skeletons of animalcules and 
minute vegetable organisms, whose geometrical forms are remarkably varied and 
beautiful; they have also been obtained (in greater abundance than ordinary) from 
mud filling the interior of fossil oyster-shells. 
§ When placed in water coloured with indigo, they will in a short time render it 
clear, by collecting the minute particles and condensing them into a solid form, 
