1922] Graham: Wing Venation of Coleoptera 193 



correlation between these two structures, but it seems to be 

 more probable that folding was a modification coming after 

 the development of wing veins and that the position of the 

 folds was influenced greatly by the position of the veins. The 

 folds naturally would follow along lines of least resistance, 

 thus bringing about a mutual adjustment of position between 

 folds and wing veins. 



As a rule the folds lie parallel to veins, but if the venation 

 becomes so modified that a fold must cross a vein the result 

 is often a thinning if not an actual break in the vein at the 

 point of crossing, similar to the bullae so common in the 

 Hymenoptera. The crossing of a vein by a fold is usually 

 nearly at right angles in the order Coleoptera. 



TRACHEATION AND VENATION. 



In most orders of insects the tracheation of the pupal wing 

 furnishes the key to the wing venation, but in the Coleoptera 

 the tracheation is of little assistance. In this study the trachea- 

 tion of only a few species has been examined, but in these there 

 was considerable variation within a single species, {Tribolium 

 cojifusum) . Further study may show a correlation between 

 these structures in the more primitive types, but for the present 

 we may assume that the primitive position of the tracheae 

 is probably better indicated by the position of the wing veins 

 which, in some groups of this order approach very closely the 

 primitive hypothetical type of Comstock and Needham. 



HYPOTHETICAL PRIMITIVE COLEOPTEROUS TYPE. 



By the comparison of a large series of wings representing 

 most of the families of the Coleoptera it has been possible to 

 develop theoretically an hypothetical primitive type of venation 

 for this order which does not differ greatly from the hypothetical 

 primitive type of the class Hexopoda as proposed by Comstock 

 and Needham. The Coleopterous type is characterized by 

 a single branched Sc, a fusion of R3 and R4 at their tips, and 

 by a similar fusion of R5 and Mi. Also the first forks of R, 

 M, and Cu are typically well toward the base of the wing. 

 (Fig. 1). 



