NO. 1438. WINGS OF THE TENTHREDINOIDEA—MAcdlLLIVRAY. 605 



are fastened by a series of hooks on the costal margin of the hind 

 wing which fasten into a fold along the hind margin of the front wing. 

 These hooks may extend from the base of the wing to near the middle 

 of the cell R1+.3, they may be arranged in two groups, one near the 

 base of the wing and another near the base of the cell K,+.2, or they 

 may be arranged in a compact group near the base of the cell Ri+g. 

 In all cases this latter group is alwa^^s the strongest, and lieing situated 

 near the middle of the wing exerts a strong influence on the course of 

 the veins found in this region in both wings, as will be shown later. 



The path of the tip of an insect's wing during flight is that of a fig- 

 ure 8 (fig. 14). This has been shown by Marey and other investigators. 

 It is a well-known fact that during flight the wings go through two 

 distinct motions, a stroke or downward motion and a recovery or 

 upward motion. The relation of the strike and recovery are shovvn on 

 the accompan3nng figure copied from Marey. The up 

 and down motion is due entirel}" to muscular action while 

 the resistance of the air ''effects those changes in surface 

 obliquity which determine the formation of an S-,shaped 

 trajectory by the extremity of the wing." 



From a mechanical standpoint, so far as insects are con- 

 cerned, the act of flight is really a simple one. The wing- 

 is so constructed that there is a rigid front margin for 

 striking the air and '"a sort of flexible sail behind," which 

 inclines the wing at the most favorable angle. This is 

 usually about 4.5^. During the downward motion the 

 wing is expanded to its fullest extent by the resistance | 

 of the air beneath it, while during its recover}^ it is con- 

 tracted by being folded or corrugated along the lines of fig. 14.— wing 

 the wing furrows, which in this way reduce the amount 

 of surface of the wing and consequently reduce the resistance during 

 recovery. 



The wings of most insects are corrugated or folded along certain 

 lines. In many orders these furro\vs are so persistent that they have 

 been named. Although they are not so constant in position as the 

 veins, yet they occupy so nearly the same j-elative position that it is 

 generally possible to homologize them. The function of the furrows 

 in an insect's wing are twofold, to strengthen it and to make it flexible. 

 The latter function seems to be their only use in the wings of the 

 Tenthredinoidea. In this superfamily all the following furrows are 

 present. 



The anal furiwo. — This is a longitudinal furrow extending from 

 the base of the wing to the margin just in front of the first anal vein. 

 It is distinct in both wings. In the front wings it separates the free 

 parts of Cu.j, M^+i'Ui, and M., from the vein behind the furrow and 

 has undoubtedly been an important factor in causing the atrophy of 

 the free part of these veins. 



