CRUSTACEA: AMPHIPODA 



383 



of body and in free thoracic segments. The epipodial plates are paralleled 

 elsewhere only in carboniferous species, with which these forms apparently are 

 closely allied. 



Legion III. Arthrostraca {Edriophlhalmala, Tetradccapoda). 



Although the Arthrostracan head consists of six segments, it is very short. 

 It bears six pairs of appendages, one of the normal thoracic pair being 

 added to it as ma.xillipeds. Eyes, when present, are clusters of ocelli on 

 the sides of the head. There are seven thoracic segments, the appendages 

 of which are walking feet without exopodites. The abdominal appendages, 

 when present, are always biramous; the telson never bears appendages, 

 and in the Amphipods is greatly reduced, sometimes being spht nearly its 

 whole length. The nervous system (figs. 78, 409) is of the ladder type. 

 The alimentary canal is straight and has an anterior enlargement, the 

 chewing stomach, behind which empty one or more pairs of long liver 



Fig. 409. — Male Orcheslia cavimana (after Nebeski). a', a~, antennEe; ao, aop, 

 anterior and posterior aorUe; c, heart; d, digestive tract; ,§", brain and eye; h, testes; 

 fe, gills; kf, maxilliped; I, liver; m, excretorj' organ and mandible; n, ventral nerve cord; 

 o, rudimentary ovary; vd, vas deferens; I-VII, thoracic feet; 1-3, anterior, 4-6, pos- 

 terior abdominal feet. 



tubes, while in a few Amphipods a pair of excretory tubes {m), the so-called 

 Malpighian tubules, empty into the intestine near its end. Respiratory 

 and circidatory systems vary so that they are best described in connec- 

 tion with two orders. 



Order I. Amphipoda. 



The Amphipods are almost exclusively aquatic, a few species living 

 on the shore near high-tide mark. A few live in fresh water {Gammancs* 

 Allorchestes*), the majority being marine. On land they move by a 



