distance behind this organ are two other large glandular bodies, the use of which may also be to secrete fluid for the purpose of digestion. The œsophagus terminates in a large dilatation, into which these organs pour their contents; at its posterior end the canal is dilated into a very large elongated sac, which extends backwards to about one-fourth of the length of the whole animal, and is filled with food, while from its anterior, or upper surface, it has an oval, muscular formation, from which the alimentary canal is continued forwards, and, after making a few turns, passes backwards, in an almost direct line, on the upper surface of the large sac, again passing backwards and forwards, until it finally arrives at its termination, which it passes round, and then proceeds, in a direct line, to the anal outlet. In the lower portion of the œsophagus, and also in the sac, distinct portions of woody fibre of an extremely minute character were found by the aid of the microscope of a power of three hundred, and this was the character of the whole of the contents of the alimentary canal. The _teredo_ lines the passage in the wood with a hard shell; this shell is formed around, but does not adhere to the body; it is secreted by the external covering, which, in its first formation, is extremely fragile, but becomes hardened by contact with the water, and adheres to the wood, from which it may, however, be easily detached. The interior of this shell is not filled by the body of the _teredo_, but a large space around it is occupied with water, admitted through the small orifice in the surface of the wood through which the animal first entered; the water being drawn through the respiratory tubes, into the bronchial cavity of the body, is expired again through the same orifice, and this, in conjunction with the valve-like shells attached at this part, induces a current round the animal which removes the excreted fœtal matter. The shells are very smooth on the inner surface, but are somewhat rougher on the exterior; they are much harder and firmer in the cells of the older animals than in the young ones, and are composed of several annular parts, differing greatly in their length. It is no less curious than wonderful to observe the mysterious instinct which apparently regulates the mechanical skill of the _teredo_, its own body supplying it with an implement of such admirable consistency and adaptation as to enable it to excavate a habitation for itself, so accurately formed that to a casual observer it would appear a mystery how so perfect a circle could be produced. It is only on examination that the raised and hollow parts of the wood become visible, and explain, in some degree, the auger-shaped contrivance that has been used for the purpose of perforating.