PROCEEDINGS OF SECTION D. 245 
We are indebted to Dr. Dall for an ingenious explanation of 
the real function of this rudimentary shell. He points out (m) 
that without a hold-fast the foot of the shipworm could exert no 
ressure on the wood. The requisite grip is obtained by opening 
the valves and holding them apart against the wall of the 
tube. With the fulcrum so obtained, the foot gains power to 
rasp at the end of its hole. This view that the shell acts as a 
fulcrum is, of course, incompatible with the view that it is a 
boring tool. 
Deshayes decided that it was impossible for a shipworm to 
carve out its abode with the valves of the shell, and suggested 
that certain chemical secretions of the animal might be capable 
of dissolving the wood. Exactly what that chemical agent was, 
or how it operated, was not explained. To the advocates of this 
hypothesis De Quatrefages replied, that such a solution would act 
differently upon different materials, whereas the resinous and 
ligneous layers of pines and various woods of different hardness 
and density are cut evenly and alike, and that such a solvent 
would present a rough and half-consumed layer at the point of 
attack, but none such is found. 
Therefore, continued De Quatrefages, it is obvious that the 
shipworm’s bore, as smooth and even as if cut with the sharpest 
gouge, must result from mechanical means, the means being 
friction, and the agent the foot. The foot of the shipworm is 
a highly modified and powerful organ. Its shape, that of a disc, 
is much modified from the usual Pelecypod type, in accordance 
with the work it has todo. It is capable of considerable exten- 
sion and lateral movement, and in natural position is applied 
to the end of the burrow, the seat of operations. 
An apparent objection to the idea that the foot is the in- 
strument of perforation is that it is softer than the wood. 
It is, however, within the experience of all that harder sub- 
stances may under certain circumstances be abraded by 
softer. A well-known instance is the toe of the statue of St. 
Peter, in Rome, worn down by the kisses of generations of wor- 
shippers. The foot of the shipworm is aided by working under 
water on a macerated surface, and its substance is capable of 
being renewed as fast as it wears away. Hancock* has shown 
that the foot contains calcareous bodies such as have been proved 
to occur in the skin of other Mollusca. 
It is not generally known that the boring of the Cobra is 
audible. But most waterside folk can from experience indorse 
the following statement of Lamb:—“ On a still summer night 
IT have heard them grinding their way into the wood, and the 
noise of their grinding would surprise you if you should put 
your ear to the head of a pile in which they were at work (7).” 
(m) Dall. Trans. Wagner Free Inst., iil., 1895, p. 498. 
(*) Hancock. Annals and Mag. Nat. Hist., Oct., 1848, p. 225. 
(n) Lamb. Trans. Am. Civil Engineers, xxxi., 1894, p. 239. 
