and watched its eating, the Worm appeared after a few moments, aware probably by the vibrations of its huge fellow-tenant's body, that feeding was going on, and not I think by any sense of smell, for a reason which I shall presently adduce. The mode and the place of the Worm's appearance were the same in every case, and it invariably glided to the Crab's mouth between the two left foot-jaws. I was surprised to observe what a cavern opened beneath the pointed head of the Nereis when it seized the morsel, and with what force comparatively large pieces were torn off and swallowed, and how firmly the throat-jaws held the piece when it would not yield. Occasionally it was dragged quite away from the Crab's jaws, and quickly carried into the recesses of the shell; sometimes in this case he put in one of his claws and recovered his morsel; at others he gave a sudden start at missing his grasp, which frightened the Worm and made it let go and retreat; but sometimes the latter made good his foray, and enjoyed his plunder in secret.
The worm is itself a striking and even handsome animal; and there is in its colours and their distribution,—two bright white lines running through the whole length on a light red ground,—a curious similarity to the colouring of the Crab.
I have reason to think that the partnership in question is by no means casual or exceptional, but ordinary if not constant. A second Whelk-shell in my Aquarium, surmounted also by a Parasitic Actinia, but which has been deserted by the Soldier, retains a Nereis as its tenant: and I know from experience
