STUDIES OF VARIATION IN INSECTS 231 



over " the thickened anal (hinder margin) of the middle one- 

 third of the fore wing. The fastening together of the wings dur- 

 ing flight so as to insure perfect synchronity of movement and 

 to effect practically a one-wing-on-a-side specialization is not 

 unique with the bees, but occurs among other Hymenoptera, as 

 the ants and wasps, also in the caddice flies and jugate moths, 



FIG. 21. Part of costal margin of hind wing of honey bee much magnified, 

 to show hooks. 



where the joining of the wings is loose and little perfected, de- 

 pending on the overlapping of the base of the hind wing by the 

 backward projecting subtriangular flap or " jugum" of the base 

 of the fore wings, and also among the frenate moths by the 

 well known frenulum or "bridle." This- tying together of the 

 fore and hind wings is, in effect, a step toward that specializa- 

 tion shown by the Diptera, the possession of but a single wing 

 on each side. In the swiftest and most effective flyers among 

 the Lepidoptera, the hawk-moths (Sphingidas), the hind wings 

 are greatly reduced, being indeed wholly subordinate to the 

 fore wings, on which the flight function really depends. Among 

 the Hymenoptera, too, this specialization has gone far so that 

 in the ants and the bees the marked reduction in the size of the 

 hind wings and their perfect attachment to the fore wings by 

 means of the hooks and anal ridge contrivance result in subor- 

 dinating them wholly to the fore wings. Without doubt the 

 effective flight of the honey bees depends largely on this par- 

 ticular specialization of the flight organs, so that the costal 

 hooks of the hind wings on which the perfect tying together of 

 the wings depends, are to be looked on as important structures, 

 small and simple as they are. Flight has everything to do with 

 the successful life of the bees, and the costal hooks have much 

 to do with successful flight. An optimum condition of number 

 and character of costal hooks is certainly advantageous to the 

 bee ; variations from this optimum are to be looked on as dis- 

 advantageous. Natural selection ought to find in the variation 



