182 TEREDO. SIIIP-JVORM. 
peculiar sl;in, and furnished materials, by its junction with 
the tube, for gradual elongation in its progress through the 
wood. ,11 * 
Against this doctrine, we are aware that the theory of ac¬ 
tual mechanical action, as supposed by Sir Kvenud Home, 
in the Philosophical Transactions for 1806, will be natu¬ 
rally opposed to us. Deference to authority so respect¬ 
able, will at all times make us diffident of our own opi¬ 
nions in contravention : but as the subject, in our piesent 
state of the physiological knowledge of this class of ani¬ 
mals, is little more than speculative 5 and as the inquiiy 
comprehends a curious investigation of singular animal 
economy, we will venture to make such remarks as have 
occurred to us. , 
Comparative reasoning will support us ; since it cannot 
for a moment be supposed, that the Pholas, a tiihe \eiy 
much approximating to the Teredo in habits and proper¬ 
ties, make their still more considerable excavations, both 
in wood and stone, by any mechanical piocess. Still less 
is the probability, or even possibility, of many others which 
are known to inhabit the interior of rocks, as the Arcaper- 
forans, Mya distorta, Venus perforans, Solcn minutus, and 
even the Ostrea sinuosa, to form and expand their cham¬ 
bers, except by a solution of the substance around them. 
The action of boring, as by a centre-bit, against the grain 
of oak hardened by a long lodgement in salt water, must 
suppose a power not very compatible with the mere gela¬ 
tinous substance of which the upper part of this animal is 
composed, unfurnished with the necessary apparatus for 
muscular resistance, and where at least one complete cir¬ 
cular volution of the instrument must be made. Ilut to 
put the question, as we think, beyond all doubt, the inter¬ 
nal termination of every perforation, and we have some 
hundreds before us of all sizes, is spherically concave, and 
not abruptly truncate, which must be the case if it were 
effected upon the principle of a centre-hit. 
We are also inclined to suspect from analogy, that the 
Teredo gigantea has its larger termination in some calca¬ 
reous substance, probably a soft sandstone or limestone. 
Presuming therefore upon the foregoing observations, we 
have been induced to draw our specific distinctions princi¬ 
pally 
