ON A NEW ICHTHYOXENUS FROM LAKE 1ÌIWA. 



I29 



coarser on cxopoditc than on endopodite. Endopo dites arc of a darker 

 appearance than exopodites. 



Uropods (fig. 9) prominently standing out bothways from terminal 

 metasome segment. The uropod itself also distinctly branched ; both 

 rami rod-like, rounded at end, without hairs or tooth-like processes ; 

 exopodite always much longer than endopodite. Length of uropods 

 approximately equal to or a little greater than, the length of terminal 

 metasome segment. 



Measurements of the body of typical adult female : 



Length Breadth 



Cephalon 1.16 mm. 1.87 mm. 



Mesosome 7.39 „ 5.52 „ 



Metasome 4.63 „ 4.56 „ 



Total 13.18 „ 



A number of adult females measured ranged in length of body 8-143- mm - 

 and in breadth 5-6 mm. 



The posterior part of body in female is bent more or less to one 

 side, either right or left. This feature is however not so much pronounced 

 as in /. japonciisis. It seems the bending stands in certain relation with 

 the side of host body on which the dwelling sac opens : it takes place 

 invariably towards the side of same denomination as that of the fish body 

 on which the orifice is situated. 



Adult male. — Males differ considerably from females in external 

 appearance. They are of a more slender and symmetrical form than 

 females, the bending of body being scarcely ever shown in this case. 



The males usually have somewhat larger eyes than the females ; they 

 are situated decidedly more closely together in the former than in the 

 latter. Thoracic legs usually better developed in males than in females. 

 Mouth parts are of a similar structure in both sexes. The same may be 

 said of pleopods ; only, those of males are slightly narrower. The 

 " appendix masculina " of second pleopod is comparatively longer, its free 

 end almost reaching the posterior end of endopodite. The terminal 

 segment of metasome is also comparatively longer. 



