THE ADULT DRAGONFLY 17 
This may seem a bit puzzling at first glance. It long was so to 
entomologists. The puzzle was solved by studying vein origin. Wing 
veins develop about the air tubes or tracheae that traverse the wing 
buds of the dragonfly nymph. Chitin is deposited about these tracheae 
forming the stiff, rod-like but hollow supporting veins, while the areas 
between expand and become thin membrane. Crossveins develop 
late; so that if one examine with a microscope the wing pad of a well 

Fic. 5. Tracheation of nymphal wing of Gomphus. 
grown (but not full grown) dragonfly nymph he may see the course 
of the antecedent tracheae very clearly. The accompanying sketch 
shows clearly the tracheae of the six principal veins. It shows also how 
the three cross connections at stigma, nodus and triangle are formed. 
The stigma is merely a thickening—an area of heavy chitin deposition. 
The subnodus (sn), oblique vein (0) and bridge (br) are all formed 
about the base of the radial sector. Arculus (ar) and triangle (¢) are 
initiated by basal bends in media and cubitus respectively. These 
bends are very gentle at first and become sharply angulated only in 
the adult wing.* 

Fic. 6. Region of arculus and triangle in Zygopterous wings. 
Such is the plan of the venation of the dragonflies (suborder A nisop- 
tera): that of the damselflies (suborder Zygoptera) differs only in 
small particulars. The most marked difference is in the cubital vein, 
which does not bend sharply backward to form a triangle but runs 
directly outward to its place of forking. There its posterior branch 
(Cuz) is offset to the rear and angulated at its junction with the tip 
of the anal vein. There is no “‘triangle’’ in the damselfly wing. Instead 
* This matter was discussed and illustrated more adequately by the senior 
author in Proc. U. 8. Natl. Mus. 26: 703-764, 1903. 
