Sexual DinimjMsm in the Butelid genus Parastasia. 497 



processu mesosternali nullo, scutello puuctato, fere semicirculari ; 

 elytris brevibus, postice paulo ampliatis, rugose punctato-striatis ; 

 pygidio rugoso-punctato ; abdominis segmento primo subtus feiuor- 

 umque posteriorum macula obscure rufis, horum margine superiore 

 prope apicem acute angulato. Long 13 — 17 m.m. 



^ pygidio lajte rutb, tarsorum medioruni et posticorum unguibus 

 externis apice tissis ; ^ pygidio nigro, nonnuuquam linea media 

 obscure rufo, tarsorum mediorum et posticorum unguibus externis 

 basi dente minuto. 



JIab. S. Japan : Oshima. 



It will be seen from this account that sexual dimorphism 

 is almost universal in this genus and the forms which it 

 takes are very varied. In about half the species the 

 claw-structure differs according to sex, but upon no uniform 

 plan, although, contrary to the condition found in the 

 dimorphic insects I have already described belonging 

 to the Anomalinffi, the males invariably have the claws 

 more divided when there is a difference. In colouring, 

 whereas in that gi-oup the male is almost invariably 

 darker than the female, the reverse again seems usually 

 to occur in Parastasia, the female being in many cases 

 quite black while the male is more or less marked 

 with red or yellow. In P. Unotata however the black 

 female alone possesses light markings, the male, rather 

 lighter in ground-colour, being without them. Other 

 strange sexual characters noticed here are the modified 

 middle tarsus in the male of the group last mentioned, 

 the deep grooves on the elytra of the female P. canahculata 

 and P. miraUlis, the sternal process of the latter, the 

 presence of hairs on the pygidium in the females of two 

 species, the peculiar sooty propygidium of others, and the 

 differentiated cephalic horns in the " heterocera group. 



These facts show that, whereas, in general, secondary 

 sexual modilications are restricted to the male, in the 

 aenus Parastasia they occur in about an equal degree m 

 both sexes. As to the meaning of the phenomenon it 

 seems premature as yet to speculate. There is no doubt 

 that it is of much more frequent occurrence than has been 

 generally supposed and that the forms it assumes are 

 more varied than has yet been revealed. Until these are 

 more completely known no explanation can be final. Mean- 

 while it will be well if entomologists will devote more atten- 

 tion than they have hitherto done to the question of sex. 

 TRANS. ENT. SOC. LOND. 1899.— PART lY. (DEC.) 33 



