Page:The common shells of the sea-shore (IA commonshellsofse00wood 0).pdf/25

Rh are still horny and closely feathered, but are short and rather variable in form. At fig. 3 are drawn the valve and pallets of another species, Teredo malleolus, in which the pallets are of shell, and shaped something like battledores. The general form of the shell is well seen at fig. 4, which shows the interior of the shell, so as to exhibit the curved process at the hinge and the method by which the two valves are united. This is the portion that was once mistaken for the jaws.

The Teredo is not very particular as to the kind of timber into which it bores, but always goes with the grain, unless it meets with some obstacle, such as a nail or a very hard knot; and in such a case it turns out of its track for a short distance, and then resumes its former course. As it bores its way along, it lines the tunnel with a coating of shelly matter, technically named "the tube," which has no connection whatever with the animal which makes it. When it is allowed to work undisturbed, as is the case with submerged piles and floating timber, it makes terrible ravages, gnawing away the wood, and rendering a huge mass of previously sound timber a mere mass of light shells, in which not an inch of uninjured wood can be found.

The tube is white, and very thin, though stronger than its thinness would seem to indicate. In the Teredo norvagica the tube is remarkable for a singular structure, which is shown at fig. 6. The tube is very long, narrow, and runs a somewhat winding course. The narrow end of it is divided into a number of compartments, by ten or twelve thin partitions which traverse it, but which do not form absolutely separate chambers, inasmuch as each partition has a tolerably large oval hole in the middle.

As is the case with the Pholadidea, the Teredo passes through several changes of form, and in its earlier stages is wholly unrecognisable by anyone except a practised naturalist. It is very minute, nearly sphe-