CRUSTACEANS Gammarus pulex (Linn.), to which Dr. Hamilton calls attention in a passage already quoted. Less economically useful but scientifically of more interest are the * well-shrimps.' These may be regarded as the one redeeming feature in the niggardly annals of Berkshire carcinology, for though the earliest discovery of them was made in another part of England, it was through Berkshire specimens that they were first recog- nized as a determinate part of our English fauna. Bate and Westwood, in their History of the British Sessile-eyed Crustacea^ when discussing the genus Niphargus^ Schiodte, write as follows : Between the years 1835 and 1842, Koch, in the continuation of Panzer's great work on the Insects of Germany, published descriptions and figures of two species which he procured from the draw-wells of Ratisbonne and ZweibrUcken, under the single name of Gammarus puteanus. In 1851 Schiodte obtained other specimens from the caves of Carniola ; and to him is due the credit of establishing this interesting genus among the Amphipod Crustacea. In the year 1852 Prof. Westwood was so fortunate as to obtain from a pump with a substratum of clay, near Maidenhead, a quantity of these animals. 1 The specimens forwarded to Prof. Westwood from Maidenhead proved to belong to the species Niphargus agui/ex, Schiodte, and this, which is possibly but by no means certainly identical with Gammarus subterraneus, Leach, 1813, was soon afterwards found to occur in the wells of several counties. 8 That all the Malacostraca are tied and bound together in singularly close relationship is not readily apparent to those ' that choose by show, not learning more than the fond eye doth teach.' The eye must be not ' fond ' in the old sense of simple and foolish, but well informed, before it can perceive the resemblances that connect the groups together, or even duly appreciate the features that keep them distinct. The Amphipoda to which Gammarus and Niphargus alike belong have as a rule all the same parts and appendages as the shrimp of commerce, with one excep- tion. The eatable shrimp, like the crayfish and the crab, has pedunculate eyes. According to the length of the stalk, the depth of the orbit, and other arrangements, movable organs of vision are capable of playing a great part in the activities and appearance of species which possess them. But this does not affect the Amphipoda, all of which have the eyes sessile. They cannot, like a poet in a fine frenzy, roll them to and fro, nor like a decapod abruptly lift or lower them. These unjointed eyes cannot take rank in the series of appendages, and accordingly they cannot be supposed to imply a supporting body-segment. In the head and thorax of an amphipod therefore there is no proof of more than thirteen segments, and the last seven of these are not covered by a carapace or immovably consolidated. By the intervention of a flexible membrane they are after a fashion articulated one to the other, with the same freedom of movement as that which pertains to the segments of the abdomen both here and in the lobsters and true shrimps. Of the limbs corresponding to the seven segments of the thorax or perason, the first two 1 Brit. Sess. Crust, pt. 7 (1862), i. 312. * Loc. cit. p. 317. 127
