438 



ARTUBOPODA. 



Legion III. Arthrostraca {EdriojMhahnata) . 



Although the head of the Arthrostracau consists of six seg- 

 ments, it is remarkahly short. It hears six pairs of appendages, 

 one of the normal thoracic pair heing added to it as maxillipeds. 

 Eyes, when present, are aggregates of ocelli situated on the sides 

 of the head. There are seven thoracic segments, the apipendages 

 of which are walking feet which lack exopodites. The abdominal 

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

 bearing ajipendages, and in the Am2:ihipods is greatly reduced, 

 sometimes being split nearly its whole length. 



The nervous system (figs. 75, 448) is of the ladder type. The 

 alimentary canal is straight and has an anterior enlargement, the 



F.G. 448.-Ma,lc Orchestm. cavivinna. (After Nehcski.) n'. <i\ antenmi? ; .7,., now, 

 anterior aiul posterior aortaa ; 0, heart; ,l,,\vje>tivv tract; y, brain and ere; Ji, 

 testes ; It., mils; hf, maxiUiped ; I, liver; m, rxrretca-x- ..rtcan; h, ventral nerve'cord- 

 n, rudimentary ovary; m(, vas deferens; /-IT/, tln.raeie feet; !-:. anterior, 4--;, 

 posterior abdominal feet. !••-> 



chewing stomach, behind which empty cue or more pairs of long 

 liver tubes, while in a few Amphipods a pair of excretory tulies, 

 the so-called Malpighian tubules, empty into the intestine near its 

 end. Kespiratory and circulatory systems vary so that thev are 

 best described in connexion ^yith the two orders. 



Order I. Amphipoda. 



The Amphipods are almost exclusively aquatic, a few species 

 living on the shore netir high-tide mark. A few live in fresh 

 mitn- ((;,i,iiiiu/rvy, AUorchestes), the majority being marine. On 

 huid they move by a leaping motion, whence the common name, 



