To the Stalked-eyed Crustaceans belong the Prawn, the Shrimp, Mysis, or the Opossum Shrimp, and the Crabs, to mention only those forms with which we are dealing here. The reason for scientific and popular names will be evident if living or spirit specimens are examined, for it will be seen that the eyes are elevated on stalks. Mr. Stebbing[43] relates an amusing story of a very intelligent student, who, on being told that the eyes (of the shrimp) were stalked, candidly confessed to having always thought that this appearance was due to their having been forced out of the head by boiling. The general shape of a Prawn (_Palaemon serratus_) is fairly familiar to everybody. The body is divided into two principal regions--the carapace, or cephalothorax, as it used to be called (formed by the union of the head and thorax), and the pleon, or swimming part. The carapace has a projecting beak or rostrum, and is unsegmented; the pleon is divided into segments, and the whole may be represented thus:-- ---- -- -- -- -- -- -- ) _c_ 1 2 3 4 5 6 _t_ where the long stroke (_c_) stands for the carapace, the shorter ones (1–6) for the segments of the pleon, and the ) for the telson or tail. The carapace consists of fourteen united segments, and this will give twenty or twenty-one segments in all, according as we reckon the telson an appendage of the sixth segment of the abdomen, or as a distinct segment. The carapace bears the eyes, two pairs of antennae, six pairs of mouth appendages, and five pairs of walking legs or perei´opods, normally with seven joints--in all, fourteen pairs of appendages, that is, one pair for each of the fourteen segments of which the carapace is composed. The segments 1–5 of the ple´on bear swimming feet, or ple´opods, and the female uses these for retaining the eggs, which she bears about with her. In this fashion the ‘hen’ lobster carries her ‘berries.’ The Prawn is a capital inmate of the aquarium, and as it does well in confinement, specimens should be kept in order to get a general acquaintance with their form and external anatomy, and to watch their habits. The Common Prawn will answer the purpose, but still better is _Palaemone´tes varians_, an exceedingly common species. It has this advantage, that it ‘seems to be equally at home in salt water and fresh.’ The only condition necessary is a good supply of food, and this may be furnished by putting into the aquarium from time to time a quantity of water-fleas. If these Prawns are well fed they will shed their skins at frequent intervals, and this operation will give us material for examination, for the cast skin will serve our purpose almost as well as a spirit specimen.