6 
defined mouth, and a kind of proboscis, the use of which will 
presently be explained. The anterior portion of the body contains 
the viscera; the breathing organs being, as has been already stated, 
prolonged posteriorly. The bivalve shell is remarkably small, 
covering only the anterior extremity of the body, and, being of no 
use for the protection of an animal destined to live and die en- 
closed in a chamber in which it is secure from intrusion, it becomes 
the instrument by which the creature extends its burrow. It is 
remarkable that there should have been so much doubt as to the 
mode by which the Teredo bores into the wood in which it lives. 
An examination of the hard concave shells shews that they are 
exactly adapted to the purpose; each valve being shaped some- 
what like the top of a carpenter’s auger, and having its anterior 
surface covered with minute ridges, disposed with beautiful regu- 
larity, while the microscope shews that each ridge is finely 
serrated, the minute points being different in shape and arrange- 
ment in different parts of the shell. The shells are open, or 
‘‘ gaping” both in front and behind ; the long body being extended 
through the posterior opening, while in front what may be termed 
the face of the animal is exposed; but this is almost covered by a 
kind of proboscis (already spoken of) answering to the ‘ foot,” 
with which many molluscs are furnished, the mouth being situated 
first underneath this organ. The proboscis has the appearance of, 
and is probably used as a sucker, by which the Teredo fastens 
itself. It thus acts as a centre-bit, and the animal, by moving the 
boring-shells constantly in a circular direction, is enabled to scoop 
out a channel in the wood with equisite precision and regularity, 
the concave termination of the canal being as smooth as if it had 
been polished by the art of man. 
The composition of the shell of some pieces of Pholas is stated 
to be such as would enable it to act mechanically on the hardest 
limestone ; and the shell of Teredo appears to be equally adapted 
to the work of rasping away the surface of very hard wood. 
Some kinds of wood, however, are proof against the attacks of the 
borer, among which Jarrow wood, from Australia, has been success- 
fully tested; African oak and ‘‘ Greenheart ” are also too hard for 
Teredo. 
In like manner certain kinds of stone will resist the attacks 
of Pholas—as for example, Portland stone, which contains a 
quantity of silica. 
The shells of Teredo are united to each other and to the 
animal by strong muscles, but the valves are not connected 
together by a hinge or ligament, there being no necessity for 
opening and closing the valves as in non-boring Conchifera. 
As the Teredo goes on extending with marvellous rapidity the 
chamber which forms at once its home and its tomb (for it can 
neyer withdraw itself from the excavation) it lines the walls with 
