INSECTS. 



The phenomenon known as the alternation of generations, — that is to say, 

 where produced generations alternate with each other in consecutive succession, — 



] , common oak-gall wasp ; 2, Torymus reyius, a parasite on the same ; 3, Gall of Cynips gemmce ; 4, Larval 

 chamber, shut and open ; 5, The same enlarged, above on the left is figured the purple hairstreak and its 

 larva; 6, The same enlarged ; 7, A gall cut through, showing the grub. 



2 6 4 



1, the sponge gall-wasp, with an old sponge-gall ; beneath is a new gall, whence the wasps have not yet made their 

 exit ; 2, oak-root gall- wasp, with its gall ; 3, bramble gall- wasp (Diastrophus rubi), with its gall ; 4, A gall of 

 the same slit in half; 5, Synergus facialis ; 6, Figites scutellaris, parasites; 7, Ibalia cultellator, parasitic on 

 Sirex juvencus. (All the galls and Fig. 7 nat. size ; Fig. 6 enlarged.) 



