Vol. 1.] Woodtvorth. — Wing Veins of Insects. 91 



characters embraces all of the conspicuous marks of the wings 

 of Odonata. However, with all of these wanting, the whole 

 facies of the wing is so distinctly like that of the Odonata, that 

 one would not hesitate to place it in that group. 



The enormous size of the insect requires an immense num- 

 ber of veins, but most of them are the mere duplication of 

 independents. The really characteristic veins are given in the 

 accompanying drawing (Fig. 27). At the base there are five 

 strong veins, alternately convex and concave. An independent 

 series interpolated behind the primary reaches nearly to the 

 base. We will consider rather fully the process of specializa- 

 tion of this wing, in order to lead to the consideration of that 

 of the Odonata. 



The fact is brought out clearly in this group that there is a 

 close correlation between the shape of the wing and the char- 

 acter of the venation. Shape and venation were doubtless 

 developed together, and each is somewhat dependent on the 

 other. In the adjustment between the venation and the shape, 

 the great length of the wing required the stiffening of the 

 longitudinal axis. This is the one predominating mechanical 

 necessity. All otlier matters become of distinctly secondary 

 importance. 



The Protodonatid wing is somewhat specialized in a number 

 of ways, but in nothing is this carried to the extent seen in the 

 provision for the longitudinal stiffening. The number and 

 position of the longitudinal veins can have but minor impor- 

 tance, because of the regular monotony of their shape, size, and 

 position. Many of them are scarcely more significant than the 

 cross veins. All veins are simple, except the independent 

 systems, and perhaps also the posterior, though all but two, or 

 perhaps three, of the apparent branches are in reality only 

 attached independents. 



The one important and characteristic specialization of the 

 Protodonatids, which also gives character to the venation of all 

 the existing Odonata, consists in the limitation of the basal 

 veins to five strong ones, arranged two on either side of the 

 primary. These five veins are situated on alternate elevations 

 and depressions of the membrane. All these veins are con- 

 nected by cross veins, and the whole forms a very rigid com- 

 pound truss structure. 



In passing from the base toward the apex the arrangement 



