PERFORATIONS OF MARINE ANIMALS. 45 
great numbers in the tough mucous sheaths in which an Austra- 
lian Cerianthus lives.* 
The burrowing powers of all the foregoing forms would seem 
to be well calculated to secure protection for themselves, but 
there can be little doubt that they also perform an important 
function in the disintegration of dead shells, and in corroding 
the surface of calcareous and other rocks. While they thus act 
beneficially in regard to dead shells, the same cannot be said 
with respect to their interference with the living; for as soon as 
the perforations of either annelid or sponge touch the internal 
surface, the Oyster or Limpet, for example, secretes layer upon 
layer of the nacreous substance in order to shut out what is 
evidently an irritating intruder, and thus the thickness of the 
shell is often greatly increased. 
So far marine animals have been dealt with which bore into 
various earthy substances, but others perforate wood and allied 
materials, like the Crustacea, whilst the Mollusca also do so, 
and likewise bore in rocks varying in hardness from chalk to 
granite, as well as make holes in other shells. 
Boring and burrowing are common features amongst the 
Crustacea. Thus, to take them in their order, certain Cirripedes, 
e.g. Alcippe lampas, Cryptophialus, and Lithotrya, perforate 
shells, the former attacking the columella or axis of the shell, 
while the boring sponge enters the exterior surface and rapidly 
spreads over the whorls, so that between them the shell soon 
crumbles to fragments and disappears. Its discoverer (Mr. 
Hancock) did not think Alcippe bored by its shelly plates, though 
the perforations might ‘‘result from a solvent, or from the appli- 
cation of minute cutting bodies on a highly contractile, soft, and 
pliant surface.”+ Darwint{ thought the burrowing of Lithotrya was 
mechanical, the peduncle being studded with calcified heads and 
star-headed spines, which form a rasping surface, and are worn 
away, to be replaced next moult. ‘‘ It [burrowing] is effected by 
each layer of shell in the basal attached disc overlapping in a 
straight line the last formed layer, by the membrane of the 
* Prof. Haswell, Proc. Linn. Soc. N.S.W. vol. vii. p. 341. 
+ Ann. Nat. Hist. 2nd ser. (4), p. 318, plates 8 and 9, 1849. 
{| Monogr. Cirripedia, pp. 386-348, 1851. 
