244 PROCEEDINGS OF SECTION D. 
BorInG. 
The operations of the Teredo are said to have suggested to 
Brunel, the engineer, his method of tunnelling under the Thames. 
It is of the first importance to an inquirer into the operations 
of the Cobra to know how it does its work. Yet this is exactly 
the point upon which all non-biological authors are in error, and 
upon which many zoological authorities are undecided. To the 
writer the matter appears simple and clearly demonstrable. 
Three possible methods by which the Cobra may bore have 
been suggested. Firstly, that it rasps out the wood with the 
edges of the valves—a plausible and popular mistake. Secondly, 
that it dissolves away the wood by chemical action, an ingenious, 
but unproved and unaccepted theory. Thirdly, that it wears 
away the wood with its foot, which, though the truth, has been 
generally ignored. 
The first hypothesis occurs naturally to any untrained observer. 
On extracting the animal from the tube, he remarks that the 
creature consists of a soft body and a hard shell, as the soft body 
could not dig through wood harder than itself, the shell must be 
the instrument of perforation. This simple argument is clinched 
by adding that the tube is enlarged only at the farther end, and 
it is just at that end where the shell occurs. The answer to 
this is, that if the shell has carved out the tunnel it is a tool 
which has done much service. A tool so employed would show 
traces of its work, bwt wnder the microscope the valves show no 
sign of wear. Under the lens the anterior area of the shell is 
seen to be denticulated by numerous rows of fine granules, 
giving to the surface a rasp-like aspect. Those who hold the 
shell to be a boring tool have pointed (/) to this apparent rasp 
as conclusive proof of their opinion, and ask what can be the use 
of it if not for filing wood. But the microscope exhibits these 
delicate granulations as fresh and sharp, without sign of wear, 
and it is impossible to suppose that they are so used by the 
Cobra. To a naturalist, it is obvious that this sculpture is the 
homologue of corresponding sculpture on the valves of Pholas, 
its near relation, and are an inheritance from some common 
ancestor. Its function probably is to keep the valves from 
slipping when expanded to grip the sides of the burrow. 
Had the shell been the instrument of excavation it would have 
appeared as a more imposing feature of the total organism. All 
systematists are agreed that the Teredimde are allied to the 
Pholas group. Granting which, it is evident that the evolution 
of the shipworms has been in the direction of the elongation 
of the animal and the excessive degeneration of the shell. 
Another step on the same path and the shell would totally dis- 
appear. 
(2) Cailliaud. Mémoire sur les Mollusques perforants. Harlem. 1856. Bayley. Trans. 
Am. Civil Engineers, iii., 1874, p. 165. 
