9550 Insects. 



Salix babylonica and S. pentandra. They are eminently voracious, 

 and seem as if they did their best to get through their larval stage of 

 existence as quickly as possible, for they feed without intermission. 

 Those sent to me from Voorst were received on the 5th of May, those 

 from Velp on the 6lh of July; I also found them at Sterkenburg at 

 the end of July, and near ter Wadding in August and September. 

 We always found half-grown and full-grown individuals on the same 

 tree. From the above it will be seen that it is very difficult to deter- 

 mine how many generations there may be in the course of a year ; four 

 may be looked upon as certain, — there are probably five. 



The following will serve as a description of these larvae. 



Head shining, black, fuscous between the eyes and at the base of 

 the trophi. Legs twenty. Body slender; the first segment orange 

 without black spots; the second to the tenth segments pale sap-green, 

 with three black lines on the back, the edges of which lines are not 

 even, nor emarginate, but as it were frayed out. Below the plane of 

 the white tracheal tube, which can be perceived through the skin, are 

 some oval and circular shining little black knobs, namely, on the 

 second and third segments three spots united so as to form a line ; on 

 the other segments first an oval spot, then two smaller nearly circular, 

 and below this first row a second, consisting of a small vertical elliptic 

 spot and a larger horizontal one, elliptic, and evidently consisting of 

 two joined together. The last two segments are orange and un- 

 spotted, the thirteenth in young individuals being green at the base. 

 The anal valve is orange, with two little orange spines; the ventral 

 surface yellowish green and unspotted. There are some little hairs 

 about the legs and at the anus. 



The first pair of legs is orange at the base, glassy green further on ; 

 the two following pairs greenish, with a small black spot at the base, 

 these horny thoracic legs have a thick pad on the penultimate joint, 

 the last joint being armed with a black claw. The middle legs are 

 green, unspotted ; the anal legs orange. 



The larvae did not all attain the same size ; some when full grown 

 were only fifteen millimetres long, others eighteen millimetres. When 

 they were about to change they descended to the ground and crept 

 about among the dried leaves, and shortly after constructed simple 

 cocoons of a yellow colour, which were placed close together and con- 

 nected by a loose web. Comparing these cocoons with those of the 

 preceding species, a great difference will be apparent, so as to render 

 remarkable the close agreement between the imagos. 



In the summer the larvae change into pupae within ten or twelve 



