HYMENOPTERA. 233 



abdomen, beyond which it extends some distance. It 

 consists of a long, pointed implement encased in horny 

 sheaths. The larvae resemble those of saw-flies in 

 having thoracic legs, but have no abdominal prop-legs. 

 As has been noted above in many other examples, 

 the absence of these appendages is correlative with 

 habits which have probably made them useless, and 

 they have consequently disappeared. The larvae are 

 wood-borers, and often injure shade trees. 



The next family, Cynipidae, includes gall-produ- 

 cers and a few parasites, while the succeeding fami- 

 lies, Chalcididae, Proctotrupidse, and Ichneumonidae, 

 are mostly parasitic. 



CYNIPID.^. 



These gall-flies are small insects. The head is 

 usually broad with quite long antennae, the thorax is 

 thick, and the short abdomen flattened sideways. The 

 wings have very few veins. Gall-flies usually lay their 

 eggs in living plants, each species, as a rule, selecting 

 its own particular kind. The larva produces an irrita- 

 tion in the living tissues, and an abnormal growth or a 

 gall is the result. Within this gall the larva spends its 

 life. It has Uttle need of antennae, and no use for 

 biting or piercing mandibles ; indeed, it has Httle use 

 for mouth parts of any kind, since it takes scarcely any 

 nourishment, and consequently these organs and the 

 antennae, although they still exist, are in an extremely 

 degraded condition. The nut-galls, or '^ oak-apples," 

 so common on oak trees, are familiar. Fig. 184 shows 

 the gall broken open with the larva ia) in its cell 



