larger one did not always retract when touched, but upon touching
the smaller one, both were instantly drawn in.
In examining the shell while in the wood, there appeared to be a small portion, nearly at right angles to the cylinder, sufficient only to give a passage to the two small tubes. The shell was found, when analysed by Mr. Hatchett, to be perfectly similar to that of the Teredo gigantea.
The largest of these worms was 8 inches in length ; many of them lived 24 hours after separation from the shell; in these the heart was distinctly seen to palpitate. The blood in the vessels going to the head, and also in the parts near the liver, was of a red colour; but this colour disappeared soon after death.
From the middle of the exposed part of the head proceeds a kind of proboscis. As this has no orifice in it, Mr. Home thinks it pro- bable that it adheres to the wood, and acts as a centre-bit, while the animal works with the boring shells, between which it is situated. The mouth is nearly concealed by the projection of this proboscis. The body of the animal terminates in a small double fold, forming a cup, on the inside of which are two opercula, which, when brought together, close up the shell : these opercula do not correspond to the tubes, but are in a contrary direction. In the Teredo gigantea the opercula are situated in a similar manner, each shutting up one half of the bifurcation.
Some other observations,'which our limits oblige us to omit, are made on these animals before Mr. Home proceeds to describe their internal structure as observed in the dissection. Here also we must content ourselves with mentioning the most striking circumstances, refem'ng those who wish for more particular information to the paper itself.
Into the cavity of the worm there are two natural openings; one of these is the larger tube already described, by which it receives water from the sea; the other is an aperture under the boring shells, forming a slit in a transverse direction, which Opens into the space before the boring shells.
The breathing organs are attached on the posterior surface of this cavity, and have their fringed edges loose, and exposed to the sea water, which passes through this cavity to the head of the animal. In the worms, which were examined while alive, the stomachs, which extend the whole length of the abdomen, were quite empty; but in the stomachs of some of the preserved specimens there was found a yellow-coloured pulp, which, from some experiments made on it by Mr. Hatchett, appeared to be an impalpable vegetable saw-dust. The intestine, after various inflections, terminates in the small tube, through which it empties its contents into the sea.
The heart consists of two auricles, which open into two tubes; these uniting, form the ventricle. The circulation is, of course, single; but the mode in which it is performed seems to be peculiar to this animal; the blood being thrown out from the heart, towards the viscera and the head, and carried afterwards through the ves-
