182 TEREDO. SHIP-WORM. 



peculiar skin, and furnished materials, by its junction with 

 the tube, for gradual elongation in its progress through the 

 wood. 



Against this doctrine, we are aware that the theory of ac- 

 tual mechanical action, as supposed by Sir Evcrard 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 present 

 state of the physiological knowledge of this class of ani- 

 mals, is little more than speculative ; and as the inquiry 

 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 tribe very 

 much approximating to the Teredo in habits and proper- 

 ties, make their still more considerable excavations, both 

 in wood and stone, by any mechanical process. 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, Solen minutus, arid 

 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. But 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-bit. 



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 



