CRUSTACEANS As no county is smaller than this, so also in no county has smaller attention been paid to the subjects of this chapter. Neither its living naturalists nor its ancient records appear to have considered these worth taking into account. Yet this is in no w^ay due to the narrow limits of the area concerned, nor are the crustaceans themselves more screened from observation in this than in any other inland county. Their favourite haunts are here in abundance, woods and gardens, rivers and brooks, ponds and marshes, old walls, ants' nests, and in general all the lurking-places which such a region might be expected to supply for creatures of insig- nificant size and secretive habits. As a matter of fact, most of the species likely to occur are so diminutive that their beauties and singularities appeal only to the diligent microscopist. Their economic value is for the most part indirect, as a food supply for fishes, to all of which they are doubtless welcome, while young fishes in particular have been ascertained to prey greedily on the minutest forms. The only species of our inland crustaceans which human beings care to eat is the river crayfish, Potamohlus pallipes (LerebouUet). Inquiries as to the occurrence of this little lobster-like comestible in Rutland met with rather an indefinite response. Mr. Masters, of Burley Ponds, Oakham, informed me that, so far as he remem- bered, he had come across it years ago when netting in Manton Brook. It is undoubtedly met with in the neighbouring counties, so that Mr. Masters's recollection may well be trusted, although I had no personal opportunity of verifying it. The crayfish is important as our sole inland representative of the higher Malacostraca. Among these it belongs to the Podoph- thalma Decapoda Macrura, that is, crustaceans with stalked eyes, ten feet, and long tails. The 'tail' comprises the last seven of the twenty-one segments which theoretically constitute the whole malacostracan body. In point of size the crayfish itself makes no great show, yet no doubt, specimen for specimen, it would outweigh all the rest of the Rutland crustaceans put together, even if eventually the species should require to be numbered by hundreds. The smaller forms, indeed, are so disguised by misleading appellations that to most persons their true place in classification is quite unknown. In our inland fauna the members of the sessile- eyed group, though not microscopic, are still so indefinitely smaller than their stalk-eyed companion that the really close relationship between them is not readily appreciated. The Edriophthalma are so called because they have the eyes seated immovably in the head. They are also termed Tetradecapoda, because the feet are fourteen in number instead often. One of the orders was named Amphipoda, to express the fact that these limbs spread out round the animal in various directions. To this order belongs Gammarus pulex (Linn.), which was taken in one of the Manton brooks and elsewhere near Oakham. It is a common inhabitant of brooks and ponds all over the kingdom, and may be taken as a characteristic example of the tribe Gammaridea, which peoples the seas of the globe in great diversity. When compared with the crayfish it will be found to have the pleon or tail similarly divided into seven segments, and though the limbs of its middle body are more numerous, this difference is not so considerable as it might at the first glance appear. The first two pairs of feet in the amphipod answer precisely to the last two pairs of mouth organs in the decapod. In both cases they are really in the service of the mouth, but in Gammarus these appendages are as it were upper servants with more freedom of movement, while in Potamobius they are bond-slaves, in restricted attachment to particular duties. Another order of the sessile-eyed fourteen-footed malacostracans, the Isopoda, is more sharply distinguished from the crayfish by the position of the breathing apparatus. This in the normal isopods is relegated to the pleon, with which it has nothing to do in the previously- mentioned orders. Here, moreover, the seventh segment of the tail, known as the telson, is fused with the sixth segment, ratlier as the rule than as elsewhere the exception. As in other 46
