H YMENOPTERA. 



19 



purposes they may, however, be divided into Parasitica, or those in which the 

 females are furnished with an ovipositor, and Aculeata, or those in which the 

 ovipositor has become modified into a retractile sting. 



Gall- Wasps, — Family Gynipid^. 



Of the former, or parasitic section of the suborder, our first representatives are 

 the gall-wasps {Cynipidce), all of which are small and inconspicuous insects, vary- 

 ing in colour from black to brown and brownish red. The wings are furnished 

 with few nervures, and the dark stigma on the anterior margin is absent ; while 

 in some species the females have the wings either rudimentary or altogether want- 

 ing. Of the galls so common on the foliage of trees and other plants, some are 

 produced by beetles, aphides, flies (gall-midges), and others by the members of 

 the present family and some of the Tenthredinidce. In the gall - wasps each 

 species selects some special portion of the plant for its attack, which it pierces with 



green saw-fly, Tenthredo scalaris (nat. size). 



its ovipositor, and lays an egg in the wound. As to what exactly gives rise to the 

 resultant gall, which follows sooner or later upon the wounded plant, is not known 

 with any certainty. It has hitherto been supposed that the fly injects an irritat- 

 ing fluid into the wound, but recent researches tend to show that this serves rather 

 as an adhesive security to retain the egg on the selected spot. It is probable that 

 the different stimulative irritants offered, first by the inflicted wound, next by the 

 presence of the eggs, and thirdly by the movements of the larva after it is hatched, 

 together with the action of a fluid exuded by the grub itself, all tend to produce 

 the strange modifications of cell structure which manifest themselves in the forms 

 of the various kinds of galls. The larvae of the Cynipidce almost entirely feed 

 internally upon galls produced on oak-leaves and the oak-blossoms. These galls 

 are entirely closed, and the grub dwells within a hard cell, called the larval 

 chamber. In some cases there may be several such chambers, as, for instance, in 

 the Bedeguar-gall on the wild rose-tree formed by Rhodites rosce. We have said 

 that each species confines itself to one portion of the plant, and the form of the 

 gall is the same ; but an exception is furnished by the galls of Spathegaster bac- 

 carum, which occur upon the leaves as well as on the flower-tassels of the oak. 



