54 



ENTOMOLOGY 



Rl 



Coccidae have on each side a bristle that hooks into a pocket on the 

 wing and serves to support the latter. In many muscid flies a doubly 

 lobed membranous squama occurs at the base of the wing. 



In Hymenoptera the front and hind wings of the same side are held 

 together by a row of hooks (hamuli); these are situated on the costal 

 margin of the hind wing and clutch a rod-like fold of the fore wing. 

 In very many moths, the two wings are enabled to act as one by means 

 of a frenulum, consisting of a spine or a bunch of bristles near the base 

 of the hind wing, which, in some forms, engages a membranous loop on 

 the fore wing. 



In the generalized moths of the family Hepialidae, the overlapping 

 fore and hind wings are held together by ajugum, projecting backward 

 from the base of the fore wing. 



Venation, or Neuration. A wing is divided by its veins, or nervures, 



into spaces, or cells. 

 Sc l Sc2 n . The distribution of the 



veins is of great sys- 

 tematic importance, 

 but formerly, the ho- 

 mologies of the veins in 

 the different orders of 

 insects were not fixed, 

 so that no little con- 

 fusion resulted. For 

 example, the term dis- 

 cal cell, used in descriptions of Lepidoptera, Diptera, Trichoptera and 

 Psocidae, was in no two of these groups applied to the same cell. The 

 admirable work of Comstock and Needham, however, seems to settle 

 this disputed subject. By a study of the tracheae which precede and, 

 in a broad way, determine the positions of the veins, these authors have 

 arrived at a primitive type of tracheation (Fig. 69) to which the more 

 complex types of tracheation and venation may be referred. 



In general, the following principal longitudinal veins may be distin- 

 guished, in the following order: costa, subcosta, radius, media, cubitus, 

 and anal (Figs. 69-73). 



The costa (C) strengthens the front margin of the wing and is essen- 

 tially unbranched. 



The subcosta (Sc) is close behind the costa and is unbranched in the 

 imagines of many orders in which there are few wing veins, though it is 

 typically a forked vein. 



M4 



3dA 2dA 



IstA 



Cu2 



FIG. 69. Hypothetical type of venation. A, anal vein; 

 C, costa; Cu, cubitus; M, media; R, radius; Sc, subcosta. 

 Pigs. 69-73 after COMSTOCK and NEEDHAM. 



