AMPHIPODA. 499 



adult animal, though the number of segments of the antennae 

 and the special form of the legs still present differences. In the 

 Hyperina the just hatched young may be without abdominal 

 f'eet and differ so much in their form from the adult that 

 they may be said to undergo a metamorphosis. 



The Amphipoda are inhabitants of all seas from the arctic 

 and antarctic zones, in the former of which they are particu- 

 larly abundant, to the equator. The Hyperina are pelagic, and 

 lead a predatory existence among the pelagic fauna (cf. p. 502). 

 Several species, borne about in ocean currents, have a very wide 

 distribution. 



The Gammarina are to a large extent littoral, but they also 

 inhabit streams, and inland lakes. 116 species have been found 

 in Lake Baikal, and they are represented in the lakes of Colorado, 

 Switzerland and Scandinavia. Some species which live in the 

 Arctic Ocean are also found in the fresh-water lakes of Norway 

 and Sweden. Niphargus, and species of the allied Crangonyx, 

 Gammarus and Calliopius, all wholly or partially blind, inhabit 

 wells and subterranean fresh- water channels in different parts of 

 the world. The Orchestiidae in general haunt the shore, peopling 

 the lines of seaweed thrown up on beaches, and some occur in 

 damp places on land. 



The Caprellina are also littoral but occur also in the open ocean 

 on floating seaweed. The Cyamina are parasitic on the skins 

 of Cetacea. 



The Corophiidae live in tubular galleries which they construct 

 from surrounding materials, and Chelura in holes which it gnaws 

 in wood, thereby damaging the submerged timbers of docks, etc. 



The large size of the deep-sea forms is remarkable, Lysianassa 

 magellanica attains 8 cm., a length which however is surpassed 

 by the much attenuated Hyperid Cystosoma Neptuni (8'4 cm.) 

 and the Oxycephalid Rhabdosoma armatum which reaches 12 cm. 

 (nearly 5 inches). 



Sub-order 1. AMPHIPODA GENUINA.* 



Amphipoda with seven distinct thoracic segments. The 



* The classification here adopted is based on that given by Gerstaecker 

 in Bronn's Klassen u. Ordnungen der Arthropoden. For the classification 

 of the Gammarina (Gammaridea) the reader should consult the description, 

 which has recently appeared, by T. B. R. Stebbing in Das Tierreich. For 

 the Caprellina (Laemodipoda) the works of P. Mayer should be consulted. 



