2l6 



THE CRUSTACEA 



Eemarks on Habits, etc. 



The great majority of Isopoda are marine, but the large group 

 of Oniscoidea are terrestrial in their habits, and many of them 

 have developed special organs for aerial respiration, as already 

 described. The Asellidae and Phreatoicidea inhabit fresh water. 

 A very remarkable assemblage of forms have recently been 

 described from subterranean waters in many parts of the world. 

 These include not only freshwater types like Asellidae nnd 



hit 



Fig. 130. 



Adult female of Portunion maenadis (Entoniscidae). A, the brood-chamber partly opened 

 and the oostegites spread out ; the abdomen is turned to show the ventral surface. B, the 

 brood-chamber unopened, showing dorsal surface of abdomen. I r, the three lobes of the first 

 oostegite on the right side ; 1 1, the same on the left side ; II r, II 7, second oostegites, right and 

 left ; III r, Iin, third oostegites, right and left ; IV, fourth oostegite ; V r, V I, fifth oostegites, 

 right and left ; ab, abdomen ; (le, vestige of antenna ; ai, vestige of antennule ; cx^, exopodite 

 of second pleopod ; ens, eudopodite of third pleopod ; eg, head, dilated into a bilobed form by 

 the " cephalogaster " ; h, cardiac prominence; mf, maxilliped ; ov, ovary ; pi, pleural lamella 

 of first abdominal somite ; th, thorax. (After Giard and Bonnier, from Korschelt and Heider's 

 Embryology.) 



Phreatoicidea, but also members of the Cirolaninae, Anthuridae, , 

 and Sphaeromidae, which are otherwise characteristically or ex- 

 clusively marine in habitat. The number of parasitic forms is 

 very large, including many of the Cymothoidae and the whole of 

 the Epicaridea, the former infesting chiefly fishes and the latter 

 exclusively Crustacea (Ostracoda, Cirripedia, Mysidacea, IsojDoda, 



