As we continue to proceed from the lower to the higher forms, we find, on the next stage of crustacean life, the numerous families of the Entomostraca; some bristly-footed (Lophyropoda), with a small number of legs and with respiratory organs attached to the parts in the neighbourhood of the mouth, others gill-footed (Branchiopoda), with numerous foliaceous legs, serving both for respiration and swimming. Some of these creatures, which are generally of such minute size as to be only just visible to the naked eye, have an unprotected body (Branchipus), but generally they are enclosed within a horny or shelly casing, which sometimes closely resembles a bivalve shell in shape and in the mode of junction of its parts, whilst in other instances it forms a kind of buckler, an opening being left behind, through which the members project. [Illustration: King-Crab.] Though enjoying a royal title, the King-crabs, or Limuli, occupy in reality but a low rank among the crustaceans, and are hardly superior in organisation to the Entomostraca. They are of large size, sometimes attaining the length of two feet, and of a very singular structure, the bases of the legs performing the part of jaws. The best-known species comes from the Moluccas, where they are often seen slowly swimming in the sheltered bays, or still more slowly crawling along upon the sandy shores. [Illustration: Sandhopper.] In the Edriophthalmia are included the lower crustaceans that have no carapace, and whose thorax and abdomen are distinctly composed of articulated segments. The numerous legs are variously formed in the different genera for springing, walking, or swimming; and respiration is executed by certain portions of the extremities, modified for this purpose in their structure. To this order belong among others the saltatorial sandhoppers (Talitrus), which so frequently jump up before our feet when walking on the wet sea-sand; the ill-famed Cheluræ and Linnoriæ, whose devastations in submerged timber almost rival those of the ship-worm, and the parasitical Cyami, which gnaw deep holes into the skin of the whale. The sandhoppers are extremely frequent on the shores of the arctic seas, where they emulate the tropical ants in their speedy removal of decaying animal substances. Thus Captain Holböll relates that, having enclosed a piece of shark's flesh in a basket, and let it down to a depth of seventy-five fathoms, in the Greenland sea, he by this means caught within two hours six quarts of these little creatures, while a vast number still followed the basket as it was hauled up. [Illustration: Chelura terebrans.] [Illustration: Limnoria lignorum.] [Illustration: Square facets of Scyllarus.] [Illustration: Hexagonal facets of Squilla.]