THE Jl'dl'M AND SQUAMAE 



123 



gin of the anterior wing, along which they play very freely when 

 the wings are in motion, slipping to and fro like the rings on the rod 

 of a window curtain." 



At the base of the hind wings of Trichoptera and in the lepi- 

 dopterous Micropteryx there is an angular fold (jugum) at the base 

 of each wing (Fig. 138) ; that of the anterior wings is retained in 

 Eriocephala and Hepialidae. 



In the wings of Orthoptera as well as other insects, the fore 

 wings, especially, are divided into three well-marked areas, the cos- 



FIG. 138. Venation of fore and hind wings of Micropteryx purpnrrlta : ;;, jugum, on each 

 wing; d, discal vein ; the Koiuan numerals indicate veins I. -VIII. and their branches. 



tal, median, and internal ; of these the median area is the largest, 

 and in grasshoppers and crickets is more or less modified to form the 

 musical apparatus, consisting of the drum-like resonant area, with 

 the file or bow. 



The squamae. In the calyptrate Muscidse, a large scale-like mem- 

 branous broad orbicular whitish process is situated beneath the base 

 of the wing, above the halter; (Fig. 94, 10 sg.~) it is either small or 

 wanting in the acalyptrate rnuscids. Kirby and Spence state that 

 when the insect is at rest the two divisions of this double lobe are 

 folded over each other, but are extended during flight. Their exact 

 use is unknown. Kolbe, following other German authors, considers 

 the term squama as applicable to the whole structure, restricting the 

 term alula to the other lobe-like division. 



