As the Hermit grows, it is necessary for him to remove from time to time into a larger dwelling. It has been stated that he will sometimes dispossess the rightful owner of a whelk-shell for this purpose, dragging him out piecemeal and eating him; but other observers deny that this ever happens, and in most cases, at all events, the Hermit is content to wait until he finds an empty shell of suitable size. After turning this over and exploring the interior with his claws, to satisfy himself that it is unoccupied, he deftly whips the unprotected hinder part of his body into the new habitation, keeping hold of the old one meanwhile, so that he can return to it if the other proves unsuitable. The Hermits are very pugnacious, and fight with one another for the possession of desirable shells, the victor dragging his opponent out and establishing himself in his place. Besides appropriating the shell of a dead Mollusc, many Hermits seem to go into partnership with living animals of various kinds, and some of these associations will be noticed in a later chapter. A number of species adopt other dwellings than molluscan shells, and some tropical Hermits, for instance, are found living in the cavities of water-logged stems of bamboo (Fig. 37); while others, relinquishing the advantages of a portable shelter, live in holes in corals or in the canals of living sponges. Although in some of these cases the body is straight, it usually shows traces of its original adaptation to a spiral shell in having no swimmerets on the left side. [Illustration: FIG. 37--_Pylocheles miersii_, A SYMMETRICAL HERMIT CRAB. (After Alcock.) The upper figure gives an end view of the animal lodged in a tube of water-logged mangrove or bamboo, its large claws closing the opening. The lower figure shows the animal removed from its shelter.] The only Hermits which have a full series of swimmerets are the primitive Pylochelidæ (Fig. 37), which come very near to what we imagine the ancestral form of the group to have been like, and can hardly be separated from the mud-burrowing, lobster-like Thalassinidea. A few Hermits have given up altogether the use of any protective covering. One of these is the Coconut Crab (_Birgus_), to be mentioned when we come to deal with the Crustacea of the land. Another is the Stone Crab (_Lithodes_--Plate VIII.) of our own seas, and its kindred, which have redeveloped shelly plates on the back of the abdomen, but carry it doubled up under the body like the true Crabs. These also preserve some traces of the original twisting of the abdomen, and have swimmerets only on one side.