Vol. 1.] Woodworth . — Wing Veins of Insects. 73 



imately bisect the areas in which they develop. The basal 

 attachment of these veins has been destroyed in wings that are 

 flexed, and this often gives rise to much uncertainty as regards 

 homologies in distant groups. Veins of another series arise 

 independently between the tips of these and grow toward the 

 base, often becoming attached and thus simulating branches. 

 Veins are shown to have a very definite relation to the plane 

 of the membrane, some being above (dorsal), others below 

 (ventral) that plane. Thus we have the so-called convex and 

 concave veins; when the alternation of these veins is well estab- 

 lished the independent veins are produced in pairs between 

 them. Somewhat allied to the independents in the method of 

 their formation are the cross veins, which are believed, how- 

 ever, to have developed simultaneously over the whole wing 

 surface and later to have undergone specialization, accompa- 

 nied by a decrease in number. 



METHODS OF MODIFICATION. 



Having traced the development of these systems of veins 

 that give character and stability to the wing, there now 

 remains the necessity of following the organ along the lines 

 of modification which have resulted in the production of the 

 various types of venation that exist in the different groups of 

 insects. 



In these diverse specializations, while each has followed a 

 course in certain respects peculiar to itself, they have all been 

 controlled by common limitations. Some of the more important 

 of these common methods of modification should be considered 

 before proceeding to the detailed review of the special types of 

 venation. 



A factor constantly influencing venation in an insect wing 

 is the coordination of the front and hind pairs. Whatever the 

 solution arrived at in any particular case, the venation can be 

 confidently expected to offer evidences of the reaction of these 

 organs upon each other. 



The original condition was doubtless one in which the 

 wings were entirely independent of each other, such as exists 

 to-day in some of the dragonflies. The only requirement in 

 these cases is that the wings shall not interfere with each other. 

 As a consequence these insects have long and slender wings, 

 and the most conspicuous difference to be observed in their 



