268. _The COMMON SHRIMP_ (Cancer crangon), _is a very small crustaceous animal, somewhat shaped like a lobster; having four antennæ, the two interior ones short and double, with two thin projecting laminæ beneath them, and on each of the large claws a single moveable fang._ _Shrimps are common in shallow parts of the sea where the bottom is sandy._ 269. _The PRAWN_ (Cancer squilla, Fig. 75), _is a small crustaceous animal, which differs from the shrimp in having a preceding and sharply serrated horn in front of its head, four antennæ, of which the two interior ones are long, and each in three divisions, and on each of the large claws two fangs._ _It is found in many parts of the European ocean._ Both these species are in great demand for the table, the former chiefly as sauce, and the latter to eat as a relish at breakfast or with the last courses at dinner. They are an agreeable repast, and more easily digestible than either crabs or lobsters. The mode in which they are caught is generally by a kind of net called a putting net, which is fixed to the end of a long pole, and pushed along upon the sand in shallow water. Prawns in some places are caught in wicker baskets, similar in shape to those which are used for the catching of crabs (263). ---- CLASS VI.--WORMS. ---- 270. _The MEDICINAL LEECH_ (Hirudo medicinalis), _is a worm-shaped animal of olive-black colour, with six yellowish lines on the upper part of the body, and spotted with yellow beneath._ _When fully extended, the leech is generally two or three inches in length. It is found in stagnant and muddy waters._ The use of leeches in medicine is to diminish the accumulation of blood in any particular part of the body. This they do by fixing themselves to the spot, forming a hole with three sharp teeth which are situated triangularly in their mouth, and sucking the blood through the wound. When they have drawn sufficient, they are easily loosened by putting upon them a small quantity of salt, pepper, or vinegar. Leeches are caught in various ways, but one of the best is to throw bundles of weeds into the water which they inhabit. These, if taken out a few hours afterwards, will generally be found to contain a considerable number. They are collected from several of the rivers in the south of England, and are kept for sale sometimes, many thousands together, in casks or tubs of spring water. This is frequently changed, and all the slime and filth which exude from their bodies is carefully washed away. It is said that if leeches be kept in glass vessels they will indicate a change of weather, by becoming at such times peculiarly restless and active. 271. _The OFFICINAL CUTTLE-FISH_ (Sepia officinalis), _is a marine animal, with somewhat oval body nearly surrounded by a margin, eight short and pointed arms, and two tentacula four times as long as the arms, all furnished with numerous small cup-shaped suckers._