S6 BRITISH APHIDES. 



gaster haccarium, several of which constructions may be 

 seen on a single leaf- vein, can only in a very restricted 

 sense be regarded as fruit buds. Again, some Aphis 

 galls rise simply out of the parenchyma of the leaf, 

 and such do not seem to be specially attached to any 

 leaf -vein. These Aphis galls have an individual 

 growth, and draw their nourishment through the 

 tissues of the leaves or stems. 



M. L. Courchet* has well represented by plates the 

 phases of growth in galls made by the Pemphigince. 

 He there shows the cellular structure altered from that 

 of the leaf, by drawings of sections through different 

 diameters. 



M. Jules Lichtenstein has written much on the 

 migratory habits of the PempJiigince.i He states that 

 he can trace a change of life and change of food in 

 several species, just as Walker did in Fliorodon Immuli, 

 which the last author says roves from the hop plant to 

 the sloe. In the same way Lichtenstein says he can 

 follow the migration of our elm-feeding kinds from 

 the leaves of that tree to the roots of grasses where 

 they hibernate. 



More evidence is desirable before we can accept this 

 sudden change of economy as an undoubted fact. 

 More strange things certainly occur in the economy of 

 insects, and we may perhaps hereafter find that some 

 of the little known root-feeders have higher develop- 

 ments in known aerial forms. 



The Scliizoneurince and Pemphigince have sporadic 

 habits, and seem to show but little forethought as to 

 securing future sustenance for their young. Some 

 species drop their young almost indiscriminately, for 

 they place their young often on plants so unfitted for 

 their nourishment, that they eventually die immature. 

 Prof. Eiley likens this apparent waste, or super- 

 abundance of life, to the wide dispersion of vegetable 

 seeds ; comparatively few of which find a nidus for 



* Courchet, ' Etude sur les Gallos, &c.,' Montpellier, 1879. 

 t Stettiner, ' Ent. Zeit.,' 1877, p. 489. 



