194 THE WORLD OF THE SEA. 
galleries, which are as though they had been excavated with a 
hard, sharp tool. M. Quatrefages has suggested the most pro- 
bable solution of the difficulty. We must remember that the 
wood upon which the animal works is always saturated with 
water—even a slight mechanical action, especially if continuous, 
would readily clear away the softened fibre. The cutaneous folds 
of the cephalic hood, which are covered with a thick coriaceous 
epidermis, are moved by four strong muscles, and this is doubt- 
less the boring instrument. The young teredo feeds upon the 
raspings of the wood. 
