Vol. 1.] Woodworth. — Wing Veins of Insects. 37 



fold of the wing and connects loosel}^ at base with one of the 

 floating sclerites of that portion of the articular membrane. 



The eighth vein is the tracheoid margin of the membrane 

 arising from about the middle of the seventh and continuing 

 at the base into the edge of the postscutellum. 



The body is highly specialized; only the mesothorax con- 

 tains important muscles of flight, those of the metathorax 

 being nearly rudimentary. The hind wings have only the 

 feeblest motion of their own anfl depend upon the front wing, 

 to which they are attached, for their effective action. The 

 wing-root is conspicuous, though relatively small and com- 

 pact. It is the only hard part connecting the dorsum and 

 pleuron, except at the extreme ends of the segment. The 

 exact nature of the* joint may be seen in Fig. 12. 



Contrasting this type of articulation with that seen in the 

 dragonfly, we notice most conspicuously the much greater 

 expansion of the notum. This corresponds with its greater 

 importance ill fliglit in insects with this type of articulation, 

 and with the more complex and eflftcient union with the wing- 

 roots. Almost as striking is the relatively small size of these 

 roots, already alluded to. The separation of the notum from 

 the pleuron is nearly as complete as in the dragonfly, but the 

 wing-roots occupy scarcely more than a fifth or a sixth of the 

 width of the articular opening, the remainder being closed by 

 soft, flexible skin. 



Not only in these more conspicuous matters are the struc- 

 tures unlike, but when one examines the details, a difference 

 will be noticeable in every item. The differences are so 

 numerous and so great that it is difficult to conceive either to 

 have been produced from the other; they point to a differen- 

 tiation at a time when the wing-root had not been specialized. 

 Starting with such an articulation as occurs in the base of a 

 gill cover, either form of wing-root could have been developed, 

 but only by growth along different lines. 



In the evolution of a wing the wing-root must first arise as 

 the result of a thinning of the wing membrane, making the 

 organ everywhere very delicate except at the base, where there 

 must be greater strength. The further perfection of the wing- 

 root consists either in the thickening of the bases of all veins, 

 so as to produce a single solid piece, or in the thickening of 

 only those veins which come in direct contact with the bear- 



