418 Insect Architecture. 



upon the leaf-stalk, and remains in the same spot till the 

 sap, exuding through the punctures, and thickening by 

 contact with the air, surrounds it with a thick fleshy wall of 

 living vegetable substance, intermediate in texture between 

 the wood and the leaf, being softer than the former and 

 harder than the latter. In this snug little chamber, secure 

 from the intrusion of lady-birds and the grubs of aphidi- 

 vorous flies (Syrphi), she brings forth her numerous brood 

 of young ones, who immediately assist in enlarging the 

 extent of their dwelling, by puncturing the walls. In one 

 respect, however, the galls thus formed differ from those of 

 the mountain-ash just described, those of the poplar having 

 always, an opening left into some part of the cell, and 

 usually in that portion of it which is elongated into an 

 obtuse beak. From this opening the young, when arrived 

 at the winged state, make their exit, to form new colonies ; 

 and, during their migrations, attract the attention of the 

 most incurious by the singularity of their appearance. 

 (J.E.) 



On the black poplar there may be found, later in the 

 season than the preceding, a gall of a very different form, 

 though, like the other, it is for the most part on the leaf- 

 stalk. The latter sort of galls are of a spiral form ; and 

 though they are closed, they open upon slight pressure, and 

 appear to be formed of two laminae, twisted so as to unite. 

 It is at this opening that an aperture is formed spontaneously 

 for the exit of the insects, when arrived at a perfect state. 

 In galls of this kind we find aphides, but of a different species 

 from the lanigerous ones, which form the horn-shaped galls 

 above described. 



LEAF-EOLLING APHIDES. 



It may not be improper to introduce here a brief sketch 

 of some other effects, of a somewhat similar kind, produced 

 on leaves by other species of the same family (Aphidce). In 

 all the instances of this kind which we have examined, the 

 form which the leaf takes serves as a protection to the 



