WINGS OF INSECTS. 



51 



lowering the wings, and another placed aslant and 

 across these for raising the wings. 



o, wing of dragon fly ; b, wing of bee ; c, wing of a house fly. 



In general, the wings may be said to be composed 

 of two membranes united together by means of horny 

 lines, which are variously termed veins, nervures( 1 ), 

 and wing bones, though not quite correctly. I prefer 

 the term rib ( 2 ). 



The wing rib is not to be considered as a bone, but 

 as a horny and nearly solid tube enclosing air-pipes ( 3 ) 

 for the purpose of expansion. The number and dis- 

 position of these ribs, which may be reckoned about 

 seven, varies greatly in different groups of insects. 



In bees, wasps, two-winged flies, and butterflies, 

 beginning at the upper edge of the wing, we find it 

 formed by a strong rib which may be termed the 

 fore-rib ( 4 ), rendered remarkable in some butterflies for a 

 hook at its base which serves as a pulley for. the tendon 

 of a muscle 



At some distance, often about the middle of the 



(1) In Latin, Neuree. (2) In Latin, Costa. 



(3) In Latin, Trachea. 

 (4) In Latin, Costa anterior or Radius. 

 D2 



