16 



THE TRACHEATION OF WINGS 



common ancestor, it was believed that such a study would reveal the more 

 important features of the tracheation of the wings of 'the primitive winged 

 insects, and, consequently, of the wing-venation of the same. 



S<^^ Sc, 



Fig. 6. — Hypothetical tracheation of a wing of the primitive nymph 

 (After C. & N.). 



The result of our studies enabled us to construct a diagram representing 

 the hypothetical tracheation of a wing of the primitive nymph (Fig. 6). 

 Since there is no doubt that the tracheae of the fore wings and of the hind 

 wings are homodynamous, a single diagram serves to represent the trachea- 

 tion of either the fore wing or the hind wing of the hypothetical primitive 

 nymph. 



In order to avoid unnecessary repetition the data tipon which our 

 conclusions regarding the probable primitive type of wing-venation were 

 based are not given here. In the discussions of the wing-venation of the 

 different orders of insects, given later, the fundamental type of the wing- 

 venation of each order is described and its con^espondence with the hypothe- 

 tical type demonstrated ; and in Chapter IV the correlation of the paleon- 

 tological data with that drawn from the study of living insects, as regards 

 the typical form of each of the wing-veins is indicated. 



In Figure 6, and in other figures representing the tracheation of wings, 

 the tracheae are designated by the abbreviations of the names of the veins 

 with which they correspond. In referring to trachese in the text they are 

 designated in one of two ways. Thus the trachea that precedes the radius, 

 for example, may be designated as the radial trachea or it may be termed 

 trachea R. The trachea that precedes the first branch of the radius is 

 designated as trachea R\ ; and other branches of the branched tracheae are 

 designated in a corresponding manner. 



It was found that the basal connections of the wing tracheas afford 

 characters of considerable taxonomic importance. In what we regard as 

 the more generalized of winged insects, i. e., in the Plecoptera and in certain 



