1897.] Mr Perkins, Notes on some Hawaiian Insects. 375 



being no transverse folding, so that they project beyond the elytra; 

 secondly in the small development of the hind-body, at least 

 in the males ; and thirdly as being furnished with three distinct 

 sets of stridulating organs. With regard to the latter the thoracic 

 arrangement for stridulation is of the usual kind. The second 

 mode by which sounds are produced, is by rubbing the bases of 

 the hind femora against the margins of the elytra. These margins 

 are specially sculptured much like a file, and the parts which rub 

 them are roughened with minute tubercles. Altogether the 

 arrangement reminds one not a little of the stridulating organs 

 of the grasshoppers, and the Plagithmysi themselves have some 

 little resemblance in general appearance to those insects. The 

 third set of stridulating organs, which were discovered and 

 pointed out to me by Dr Sharp, are on the basal joint or coxae of 

 the middle and hind legs, and they may really be considered as 

 two distinct sets, since the middle pair operate on the adjoining 

 edge of the thorax, the hinder pair on a ridge on the basal segment 

 of the abdomen. Moreover, in a specimen of P. aequalis 

 examined, the striation of the coxae on either pair of legs was 

 different, being evidently coarser on the intermediate pair. 



It is highly probable therefore that by the use of these different 

 organs a considerable variety of sounds can be produced, for the 

 sound made by the legs when rubbing against the elytra is not 

 the same as that produced by the prothorax rubbing on the 

 scutellum, and the degree of pressure, or rapidity of movement, 

 also causes a variation in the sounds. The insects run with 

 extreme rapidity over the tree trunks, when the sun shines hotly 

 on them, and often perform curious evolutions, running in short 

 curves or zigzags and ab times almost giving little leaps. It seems 

 hardly possible that such movements can be made without stridu- 

 lation, although the sounds are not audible unless the creature is 

 held in the hand. 



The small size of the hind-body may be connected with the 

 frequent great disparity of size between the sexes, for the females 

 of many of the species are often relatively very minute, and 

 probably in all the species many such individuals would be found 

 were sufficient material available for examination. While the 

 minute males are not affected by the almost rudimentary condition 

 of the hind-body, were this of the usual length, many of the 

 large males would be quite unable to pair with a large proportion 

 of the females. As it is, this is not the case, and male and female 

 will often pair though the former is several times the bulk of the 

 latter. Moreover it should be mentioned that both sexes are 

 polygamous and pair many times. It is possible however that the 

 rudimentary condition of the hind-body is in some way connected 

 with the stridulating organs. 



