376 Mr Perkins, Notes on some Hawaiian Insects. [Dec. 6, 



The extreme variation in size of a given species may be due to 

 differences in the quality of the food of the larvae, which may 

 be found in a tree which has only just fallen, or began to die, 

 while others are feeding on a tree the wood of which is in a much 

 drier condition. 



One of the most interesting points in regard to the Plagi- 

 thmysi is the extreme variability of most of the species, which 

 affects not only the colour but also the structure. The variation 

 in the latter, however, is not so readily appreciated as the colour- 

 variations, and I do not propose to refer further to it here. 

 Variation in colour is shown in various parts of the insect but is 

 more especially remarkable on the posterior femora. 



On the Island of Hawaii there are four very closely allied 

 species of the genus. Three of these, P. varians, darwinianus, and 

 lamarckianus, are found in the same locality, but each is solely 

 attached to the kind of tree on which its larva feeds. Where the 

 different trees grow side by side the three Plagithmysi may be 

 found side by side ; but in some parts of the forest only one of the 

 three trees is to be found, in which case only the one species 

 whose larva feeds on it is also found. The fourth species, P. black- 

 biirni, feeds on the same tree as darwinianus, but occurs on the 

 other side of the island. 



All of these species are variable in the colour of the femora, 

 but the variation as exhibited in a series is distinct in each. In 

 some cases the variation is so great that the extreme forms would 

 appear to be more distinct, than are some of the allied species 

 from each other. I have examined a considerable number of 

 individuals of each of these species which are here exhibited. 

 Thus of P. darwinianus, which feeds on Sophora chrysophylla, 

 an acacia, the 65 individuals all have the femora red, the apices 

 being very rarely dark. 



Of P. blackbumi which feeds on the same tree but not in the 

 same locality, 68 have these parts black, only 5 red. 



Of P. varians, which feeds on Acacia koa, 41 have the femora 

 black, 53 have the apices bright red, while 4 are nearly entirely 

 of a reddish colour. 



Of P. lamarckianus, which feeds on trees belonging to the 

 Urticacese, the legs are wholly black or reddish, probably either 

 variety being about equally numerous, the species being much less 

 common than any of the preceding. 



Thus on the whole each species divides into two or three 

 varieties without true intermediate forms. It is true that if some 

 of the individuals of P. varians be closely examined, the apices of 

 the femora are seen to be less dark (i.e. slightly reddish), but 

 these fall in naturally with the black-legged specimens, and are 

 very far removed from the brightly coloured examples. 



