I30 



SHIGEMI ISHII. 



Measurements of the body of typical adult male : 



Length Breadth 



Cephalon 1.25 mm. 1.87 mm. 



Mesosome 5.93 „ 4.81 ,, 



Metasome 3.93 ,, 3.20 ,, 



Total I I.I I „ 



A number of adult males measured ranged in length of body 5-12 mm. 

 and in breadth 2.^-5 mm. Comparing these measurements with those of 

 adult females (p. 129), it will be seen that the males are on the whole 

 smaller than the females. 



Larva. — The larva of IcJithyoxenus opistJiopterygiuvi is of a darker 

 colour than that of /. japonensis, the pigmentation growing denser 

 towards the posterior parts of body. The general body form is somewhat 

 more slender in the present species than in /. japonensis. The body is 

 strictly symmetrical. Anterior end of cephalon narrow and truncated. 

 Antennule usually eight-jointed, about 0.43 mm. long and 0.05 mm. 

 broad. Antenna frequently nine-jointed, a little longer than antennule. 

 Both antennule and antenna directed postero-laterally. Eyes oval, com- 

 paratively large, measuring 0.30 mm. in long diameter ; the shortest 

 distance between eyes o.llmm. There are only six pairs of thoracic 

 legs as in ordinary Isopod larvae. The legs are constructed similarly 

 as in adults, excepting the fact that ischium and carpus are relatively 

 small. Dactylus and propodus large and well developed. There is 

 no constant occurrence of tooth-like processes on legs. 1 * Of pleopods, 

 the first and second pairs are of nearly the same shape : exopodite more or 

 less oval in outline, endopodite slightly narrower, and both rami of a light 

 colour (fig. 10, a). Sometimes, the first pair has apparently two-jointed 

 rami, there existing a conspicuous constriction in each ramus. The third, 

 fourth and fifth pairs show a different structure. In all these, the endo- 

 podite is more darkly coloured, markedly narrower and usually a little 



1) In the larva of I. japonensis, there constantly occur on thoracic legs a few moderately 

 long tooth-like processes. 



