and Teredo Navalis. 279 
larger one, the point of the smaller turned round, and pushed 
it off, and then went back to its original situation. 
In several instances the smaller one appeared to be the 
most sensible : since by touching the larger one gently, it did 
not retract ; but on touching the smaller one they both were 
instantly drawn in. Indeed whenever they were retracted, 
they always were drawn in together. 
When the worm was confined within the shell, the orifice 
was not to be distinguished in the irregular surface of the 
wood, which was covered by small fuci. 
The worm appears commonly to bore in the direction of 
the grain of the wood, but occasionally it bores across the 
grain, to avoid the track of any of the others : and in some 
instances there was only a semi-transparent membrane, as a 
partition between two of them. 
In examining the shell while in the wood, its external 
orifice is very small, just large enough to give a passage to 
the two small tubes. The sides of the cylinder are thickest 
near its origin, becoming thinner towards the head of the 
animal. The greatest thickness met with was - 1 - of an inch. 
The canal in the wood at its termination, and for one inch in 
length, is not lined with shell, but smeared over with a dirty 
green-coloured mucus, which is also spread upon the last 
formed portion of shell. The shell was found, when analysed 
by Mr. Hatchett, to be perfectly similar to that of the teredo 
gigantea, being devoid of phosphate of lime, and composed of 
97 parts of carbonate of lime, and 3 of animal matter. 
While the animal is in the shell, alive and undisturbed, the 
head is in contact with the end of the canal in the wood ; but 
on laying the head bare, it is drawn in for an inch into the 
MDCCCVI. O O 
