The numerous family of the Paguri, or Hermit crabs, is also condemned by its formation to lead a parasitic and robber-life. The fore part of the body is indeed, as in other crabs, armed with claws and covered with a shield, but ends in a long soft tail provided with one or two small hooks. How then are the poor creatures to help themselves? The hind part is not formed for swimming, and its weight prevents them from running. Thus nothing remains for them but to look about them for some shelter, and this is afforded them by several conchiform shells, _buccina_, _neritæ_, in which they so tenaciously insert their hooked tails, as if both were grown together. So long as they are young and feeble, they content themselves with such shells as they find empty on the strand, but when grown to maturity, they attack living specimens, seize with their sharp claws the snail, ere it can withdraw into its shell, and after devouring its flesh, creep without ceremony into the conquered dwelling, which fits them like a coat when they take a walk, and the mouth of which they close when at rest with their largest forceps, in the same manner as the original possessor used his operculum or lid. How remarkable that an animal should thus find in another creature belonging to a totally different class, the completion, as it were, of its being, and be indebted to it for the protecting cover which its own skin is unable to secrete!
When the dwelling of the pagurus becomes inconveniently narrow, the remedy is easy, for appropriate sea-shells abound wherever hermit crabs exist. They are found on almost every coast, and every new scientific voyage makes us acquainted with new species. According to Quoy and Gaimard, they are particularly numerous at the Ladrones, New Guinea, and Timor. The strand of the small island of Kewa, in Coupang Bay, was entirely covered with them. In the heat of the day they seek the shade of the bushes; but as soon as the cool of evening approaches, they come forth by thousands. Although they make all large snail-houses answer their purposes, they seem in this locality to prefer the large Sea Nerites.
The famous East Indian Cocoa-nut Crab (_Birgus latro_), a kind of intermediate link between the short and long tailed crabs, bears a great resemblance to the paguri. It is said to climb the palm-trees, for the sake of detaching the heavy nuts; but Mr. Darwin, who attentively observed the animal on the Keeling Islands, tells us that it merely lives upon those that spontaneously fall from the tree. To extract its nourishment from the hard case, it shows an ingenuity which is one of the most wonderful instances of animal instinct. It must first of all be remarked, that its front pair of legs is terminated by very strong and heavy pincers, the last pair by others, narrow and weak. After having selected a nut fit for its dinner, the crab begins its operations by tearing the husk, fibre by fibre, from that end under which the three eye-holes are situated; it then hammers upon one of them with its heavy claws, until an opening is made. Hereupon it turns round, and by the aid of its posterior pincers, extracts the white albuminous substance. It inhabits deep burrows, where it accumulates surprising quantities of picked fibres of cocoa-nut husks, on which it rests as on a bed. Its habits are diurnal; but every night it is said to pay a visit to the sea, no doubt for the purpose of moistening its branchiæ. It is very good to eat, living as it does on choice vegetable substances; and the great mass of fat, accumulated under the tail of the larger ones, sometimes yields, when melted, as much as a quart of limpid oil. Thus our taking possession of the Keeling Islands, as a coaling station for the steamers from Australia to Ceylon, bodes no good to the Birgus.