388 



THE WINGS OF INSECTS 



The wings of nymphs and pupae are broad at the base, and consequently 

 the tracheae that precede the wing-veins are not crowded together as are the 

 wing-veins at the base of the wings of adults. For this reason the identity 

 of the wing-veins can be deteraiined more surely in the wings of nymphs and 



Fig. 409. — Hypothetical tracheation of a wing of the primitive nymph. 



pupae than they can be in the wings of adults. This is especially true where 

 two or more veins coalesce in the adult wing while the tracheae that precede 

 these veins are distinctly separate in the immature wing. 



A study was made of the tracheation of the wings of nymphs and pupae 

 of representatives of most of the orders of insects, and, assuming that those 

 features that are possessed by all of these must have been inherited from a 

 common ancestor, a diagram was made representing the hypothetical 

 tracheation of a nymph of the primitive winged insect, (Fig. 409). In this 

 diagram the tracheae are lettered with the abbreviations used in designating 



/?, R.^, 



Fig. 410. — A wing of Khyphus, with the veins and cells lettered. 



the veins that are formed about them in the course of the development of 

 the wing. The diagram will serve, therefore, to indicate the typical \'ena- 

 tion of an insect wing, excejDt that the trachea; are not crowded together at 

 the base of the wing as are the vein s in the wings of adults. 



