74 Mr. P. Cameron on the 



to have dimorphic larvre, but the specific distinctions be- 

 tween the forms of this genus are yet too complicated to 

 enable us to decide if the different larvae belong to the 

 same or to different species. Brischke and Zaddach* 

 (and no better authorities could be stated) describe 

 two distinct forms of the larv?e of Cwibex saliceti, Zad. 

 (lutea auct.) on Salix caprea — one brownish-red, and a rarer 

 bluish-green one. The larva of another species of Nematus 

 {histrio Lep.), is in the great majority of cases green, but 

 specimens are occasionally of a decided reddish hue, 

 although I have never seen the red predominating to such 

 an extent as wath the red form of N. caprece. 



I find that the larvJB of the various species of Chnhex and 

 Trichiosoma are not at all clearly defined, any more than 

 are the perfect insects. Dahlbom t had an idea that the great 

 variability of the images was produced by the food-plants, 

 but this I regard as very doubtful ; and it is certain that 

 some forms which Dahlbom regarded as varieties are good 

 species, presenting distinctive (although slight) characters 

 in their larval and imago states. Several varieties of 

 Cimbex sylvarum, for instance, are bred from birch, and of 

 C. saliceti from willow ; w^hile the form mentioned by 

 Dahlbom from beech is considered by Brischke and Zaddach 

 as a good species. 



c. On the Use of the Hairs on Green Larvce. — I have 

 already alluded to the difference in the mode of feeding 

 of the protected and edible larvte which feed on the 

 flat surface of the leaf. Besides this difference in habits, 

 there is a structural j^eculiarity which distinguishes them. 

 It is that the noxious larva) have bare, shining bodies ; 

 whereas the others have their bodies more or less covered 

 with pale hairs. With flat larvae, as in Camponiscus, they 

 are only along the edge, which is very projecting and 

 waved, so that the legs are entirely hid. In Nematus pal- 

 lescens the body is more cylindrical, and covered all over 

 with pale hairs, which, although of moderate length, cannot 

 be seen unless the larva be examined close at hand, when 

 it is resting on the leaf. In Cladius, again, the bodies 

 are still more cylindrical, and the hairs are longer. Now, 

 hairs of this class appear to be entirely confined to larvae 

 (generally green) which feed on the surface of the leaf, 



* Schr. ges. Konig. HI., pi. 11, f. i. 

 t Prod. Hymen. Scand, 50. 



