In some genera both hands are alike; in others the left one is the larger. In the case of hermits which live in tooth-shells, the right hand is cylindrical in form, fitting the circular opening of the shell. The other extreme is found in the genus /Cancellus/, where both the chelipeds and the first pair of ambulatory feet are ingeniously shaped, so that when closed they form a round operculum, or door, which closes the way into the compact sponge which this crab has for its carcinœcium, or house. It is interesting to note these differences and observe the perfection with which the feet are formed and jointed to suit the openings of different shells. Some genera show other adaptations to their twisted houses, the eye-stalks being uneven in length and the ambulatory feet unequal on the opposite sides. Besides this, some species are hairy and cover themselves with dirt for further protection. The exposed claws of some hermits have a special armature of spines, which make a fringe of points around the opening of the shell when the crab is withdrawn. As the hermit grows he is occasionally obliged to find a new or larger shell, and there are amusing anecdotes of the troubles he experiences at these times while house-hunting. Very often he tries several shells before he finds one to fit. There is a tradition, not, however, well authenticated, that if the shell chosen happens to be occupied by its natural owner, the crab tears out and devours the unfortunate occupant. If the desired shell is occupied by another hermit inferior in strength to himself, he proceeds to take possession by violence. He then examines carefully the empty shell, inserting his legs and feelers, and if he decides to occupy it he withdraws his abdomen from the old shell and darts it so quickly into the new one that the act of transference is difficult to follow. After walking about with the new shell it sometimes proves to be unsatisfactory and further search becomes necessary. After it is well domiciled the crab never ventures outside the shell until it is obliged to change again on account of growth, or because some stronger crab dispossesses him. The shells of hermit-crabs serve frequently as the home of other animals which live with them a commensal life. The hydroid /Hydractinia polyclina/ often covers the exterior of such shells with a brown, velvety growth. Some sea-anemones also are commensals [pg267] with hermits. /Adamsia palliata/ is always found on the shell occupied by /Eupagurus prideaux/, and never on any other. This is a European form. On our own coast a red anemone, the /Epizoanthus americanus/, found in deep water off the entire eastern shore, fastens on the shell occupied by the hermits /Eupagurus pubescens/ and /E. kroyeri/. This anemone in time absorbs the shell of its host and itself becomes its protector—an advantage to the hermit, who finds room in the yielding polyp-mass for its increasing size, and feels no longer the necessity for change of domicile.