CH. V] WASPS 127 



of the wing are the largest and their tips are curled over ; 

 but they gradually get smaller as they pass towards the 

 extremity of the wing and the tips become straight : at 

 the same time they stand out further from the margin of 

 the wing (h' Fig. 22). In addition to the hooks there is at 

 the base of the hind- wing a strong tuft of hairs (1 Fig. 21), 

 and along the margin at first short hairs (2) and then 

 longer hairs (3) projecting forward (the hooks are merely 

 modifications of these hairs). These all are pressed up 

 against the under surface of the fore-wing and assist in 

 keeping the two wings together. 



This method of interlocking the fore and hind-wings is 

 usual in Hymenoptera, but other contrivances for the same 

 purpose are found among other insects. For example, 

 most Lepidoptera have a stiff bristle or group of stiff hairs 

 (the frenulum) arising from near the base of the anterior 

 edge of the hind- wing and engaging in a chitinous catch 

 or. group of stiff scales (the retinaculum) on the lower 

 surface of the front wing. In others, e.g. Endromis ver- 

 sicolor, the Kentish Glory, members of the genera, 

 Eriog aster, Clisiocampa, Odonestis, the eggars, lackeys, 

 fox-moths, drinkers, etc., there is no definite interlocking 

 arrangement, but the basal area of the anterior part of the 

 hind-wing is expanded so as to underlap the front wing 

 for some distance and rest more firmly against it, thus 

 avoiding dislocation. The Hepialidce (Swifts) and Micro- 

 pterygidce present yet a third system among the Lepido- 

 ptera. In these a membranous or a spine-like process 

 (jugum) springs from the hinder edge of the fore-wing near 

 its base and passes under the hind-wing, which is thus held 



