CHAPTER III 



THE WINGS 



All Dragonflies possess two pairs of well-developed wings, of 

 either equal or slightly unequal size. They are elongated mem- 

 branous outgrowths from between the pleura and terga of the 

 synthorax. The fore-wings are attached to the mesothorax, the 

 hind-wings to the metathorax. Each wing is composed of a 

 chitinous non-cellular membrane, usually quite transparent 

 (hyaline) and formed of two delicate layers fused together. This 

 membrane is strengthened by numerous thickened rods or bars of 

 hard, dark chitin, known as the veins or nervures, forming a com- 

 plicated supporting network known collectively as the wing- 

 venation. As in other insects, the basis or foundation of the plan 

 of the wing-venation is formed by a number of main longitudinal 

 veins, some of which are simple and some branched. These 

 separate the wing into areas known as the wing-spaces. Between 

 the main veins and their branches, a large number of cross-veins 

 are arranged, in such a manner that the wing is finally divided up 

 into a very large number of small quadrilateral or polygonal spaces, 

 known as cells or cellules. 



The main veins in the Dragonfly wing, with few exceptions, 

 are formed along the principal tracheae of the developing larval 

 wing. The cross-veins, on the other hand, again with one or 

 two notable exceptions, are not formed about tracheae at all, 

 but appear quite independently of the latter during the last larval 

 instar. The earlier students of Dragonfly venation, amongst whom 

 de Selys was pre-eminent, studied the wing- veins without reference 

 to the larval tracheation. Hence there arose a purely arbitrary 

 terminology, in which homologies were either obscure or ignored. 

 The study of the relationships between the larval tracheation and 



