Fig. 325. — The Wood Wasp (Sirex gigas). 



XXVII INSECTA : HYMENOPTERA 433 



of fir trees, doing much damage. It is, however, rarely 

 found in Britain, though common in some other parts of 

 North Europe. 



Cynipidae (Gall 

 Wasps) 



The Gall Wasps 

 consist of small, 

 dark-bodied forms 

 with long, simple, 

 straight antennae, 

 and with very few 

 "nervures " and no 

 dark patch on the 

 wings. There is a 

 narrow petiole be- 

 tween the fore and 

 hind body. 



The insects themselves are not usually known to the 

 casual observer, who will, however, probably recognise the 

 galls which many of them cause on the oak and other 

 trees, for such galls are some of the most common objects of 

 the country-side (see Plates IV., V., and VI.). Inside these 

 galls the insects spend the first stages of their life-history. 



The galls are formed by the female Gall 



Formation ^^^P- ^^^ '^7^ ^^^i' ^gS^ i"^ the tissues of a 

 living plant, piercing a hole for the reception of 

 each, by means of the long ovipositor she possesses at the 

 end of her body. The legless grub which hatches out 

 begins at once to feed on the soft tissue around it, and the 

 irritation of the cells which is thus caused, results in their 

 abnormal, rapid multiplication. The larva and the gall 

 develop together, the former feeding on the inner tissues 

 of the latter. 



' Internal '^^^ tissues of the gall around the hollow 



Structure cavity in which the grub lies, frequently show 



of a Gall, a, considerable amount of differentiation, as in 



the spangle gall. When cut across (Fig. 326), this shows a 



layer of nutritive tissue lining the cavity in which the larva 



lies, and round this a layer of hard protective cells 



VOL. I ~ 2 F. 



