416 



INVERTEBRATE MORPHOLOGY. 



After copulation, however, the female assumes the degener- 

 ated form, while the male dies. 



3. Order Amphipoda. 



Like the Isopoda these are essentially marine forms, 

 though the genus Gammarus is aquatic and Orchestia 

 (Fig. 190) partly terrestrial, living among the wrack on sea- 

 beaches just beyond the reach of the waves. The body in 



ht 



ro 



ru 



ce 



mt 



FIG. 190. DIAGRAM OF STRUCTURE OF Orchestia cammana (after NEBESKI). 



at 1 = antenuule. m mouth. 



at 2 = antenna. mt Malpighian tubule. 



br = bran chia. oc = eye. 



ce = cerebral ganglion. r = rectum. 



ch = chelate limb. rd = reproductive duct. 



ht = heart. ro =- reproductive organ. 



I = liver-caeca. vn = ventral nerve-cord. 



the Amphipoda is laterally flattened and presents therefore a 

 very different appearance from that of the Isopoda, though, 

 as in that group, lacking all traces of a carapace. The first 

 thoracic segment is fused with the head, and in Caprella and 

 . Cyamus the second segment likewise. The appendages of the 

 head and the maxillipeds resemble those of the Isopoda, and 

 the remaining thoracic appendages are liinblike, a certain 

 number of the anterior ones frequently possessing a terminal 

 joint capable of flexion upon the succeeding one, or even 

 being chelate The five posterior limbs or the third and 

 fourth only bear epipodial lobes which serve as branchi;i>, and 



