"Masked-crab "(Corystes Cassivelaunus, Figs. 130, 131) may be known from its curious habit of sitting upright, like a dog in the act of "begging." A peculiar crab, much resembling the "Spiny-crab," is a species Fig. 131. The Female. which does not extend further south than the Isle of Man, and accordingly goes by the name of the "Northern Stone-crab" (Lithodes maia). It is covered all over with spines, like that species; the shell being of a pale red, and the spines of a darker hue. There is a group of crabs which go by the name of "Swimming-crabs," and have their claws modified for the purpose of swimming, as well as crawling along the sea-bottom. One of the commonest of these is the "Velvet Swimming crab," or "Velvet Fiddler," as it is also called (Portunus puber). There is no difficulty in separating the crawling from the swimming crabs. The former always have the hind legs round, whilst those of the latter are flattened and oar-like. The species we have just mentioned has a broad shell, or carapace, toothed in front, with the front claws covered with little tubercles. It is bright and showily coloured, although the colours soon fade after death. Off the coasts of Devon and Cornwall this is a very common species. Its size ranges from two to three inches. Another species haunts the same habitat, but extends further along the western coasts. This is the "Cleanser Swimming-crab," whose shell is of a pale red colour. There are several other species of Portunus to be met with off the English coasts. The "Hermit-crab” (Pagurus Bernhardus), which may be found in every heap of trawler's rubbish, is one of the most singular creatures known. It takes its name from its habit of living in the empty shells of univalve molluscs, that of the common whelk being a favourite. The great peculiarity about it is that its belly, or abdomen, is always soft, and not protected by a living crust as with the lobsters. Hence the necessity for it to make up for this important deficiency by a valuable instinct, which prompts it to seek out empty univalve shells, and to thrust into them its soft and defenceless hinder part. The fore claws are covered with the usual hard crust, one of them being longer than the other, and used to block up the hole of the shell when attacked, on the plan of an operculum. Whilst the Hermitcrab is growing, these claws, &c., moult, as in the ordinary crabs, and accordingly the animal has to pull himself out of his old lodgings, and seek another and a larger. The way in which it tries each shell by inserting its soft belly into it, just as a countryman will try on half-a-dozen pairs of boots before he is fitted, is exceedingly comical. The end of the abdomen is provided with certain appendages, by means of which it can hold on to the interior of the borrowed shell. These are under the perfect control of the animal, which can let go at will. There are nearly a dozen species of British Hermitcrabs, nearly all of which inhabit different species of empty univalves. One of these crabs (Pagurus Prideaux) is remarkable for its always being accompanied by a sea-anemone, a circumstance we noticed in our chapter on sea-anemones. In addition to the foregoing, there is a group of pigmy crustaceans common in our seas, which may be found more or less abundantly in the rock-pools at low water. These belong to the family Pycno gonidæ. They seem to affect the bushy tufts of the common coralline sea-weed. In appearance they are not unlike those marine crustaceans which go by the name of "Sea-spiders." They are furnished with hooked claws, instead of nippers, by means of which they are able to cling very tenaciously to any object. One of these (Pallene pygmæa, Fig. 132) produces larvæ which have the two foreclaws, however, provided with nippers. When placed under the microscope the movements of the stomach, &c., can be plainly seen, owing to the transparency of their bodies. Their ova is attached to the abdomen by means of false feet. They do not seem to be provided with any special organs of respiration, but the oxygenation of the blood appears to take place through the general surface of the body, which is provided with perforations set in minute tubercles that are scattered all over it, like the spiracles of an insect. Notwithstanding this, the articulation of the limbs to the body is by means of stout and strong muscles, every movement of which can be seen through the transparent integument. An allied species is Achelia hispidata, Fig. 133, which may be known by its smaller and more compact body, and shorter limbs, as well as by its proboscis. It also possesses a small pair of jointed antennæ. Both the foregoing little creatures live on decaying animal and vegetable matter. The true Pycnogons, or "Sea-spiders," are now classed as genuine crustaceans by Dr. Dohrn, who has written on their embryology. One of them (Nymphon |