20 



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 regius, a parasite 011 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 then- 

 exit ; 2, OAK- 

 the same slit 

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



GALL-WASP Wlttl an Old sponge-gall , uentjuui is a. new gnuf >vj w j^v 



K-ROOT GALL- WASP, with its gall ; 3, BRAMBLE GALL-WASP (Diostrctphus rubi),. with its gall ; 4, A gall of 

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



