394 INSECT ARCHITECTURE. 



opening that an aperture is formed spontaneously for 

 the exit of the insects, when arrived at a pcrtect state. 

 In galls of this kind we find aphides, Ijut of a dif- 

 ferent species from the lanigerous ones, which form 

 the horn-shaped galls above described. 



Leaf-Rolling 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 {Jiphidcc). In all the instances of this 

 kind which we have examined, the form which the 

 leaf takes serve as a protection to the insects, both 

 from the weather and from depredators. That there 

 is design in it appears from the circumstance of the 

 aphides crowding into the embowering vauk which 

 they have formed; and we are not quite certain 

 whether they do not puncture certain parts of the 

 leaf for the very purpose of making it arch over 

 them; at least in many cases, such as that of the 

 hop-fly (^Jlphis humnli), though the insects are in 

 countless numbers no arching of the leaves follows. 

 The rose-plant louse, again, (Jlphis rosce,) sometimes 

 arches the leaves, but more frequently gets under the 

 protecting folds of the half-expanded leaf buds.* 



One of the most common instances of what we 

 mean occurs on the leaves of the currant-bush, 

 which may often be observed raised up into irregular 

 bulgings, of a reddish-brown colour. On examining 

 the under side of such a leaf", there will be seen a 

 crowd of small insects, some with and some witliout 

 wings, which are the Jlphidcs ribis in their different 

 stages, feeding securely and socially on the juices of 

 the leaf 



The most remarkable instance of this, however, 



* J. R. 



