RELLOGG: TAXONOMIC VALUE OF SCALES OF LEPlDOPTERA. 55 



scales. Primarily, I believe, the scales serve to protect and to 

 strengthen the wing-membranes. Although the membrane of the 

 wing is chitinized, it is still thin and delicate. Excepting the 

 discal vein, which, indeed, may be wanting, there are rarely cross- 

 veins in the Lepidopterous wing. There are thus left open spaces of 

 considerable area between the sub-parallel longitudinal veins. In 

 the Neuroptera, Odonata, etc., these intervening spaces are strength- 

 ened by many cross-veins. In the Lepidoptera the transverse rows 

 of scales, or rather the complete sheath of scales, may do much to make 

 good the absence of cross-veins. The veins of the wings grow 

 weaker and more widely separated as they approach the outer margin 

 of the wing, yet the wing-membrane in the broad, limbal area of the 

 wing has to endure a greater strain in flight than the membrane of 

 the discal and basal area of the wing, where the veins are large and 

 close together. There would thus exist a need, more or less impell- 

 ing, as the flight-use of the wing varied, for a strengthening of the 

 membrane of the wing. This need of strengthening would vary on 

 the different parts of the wing, the limbal area needing it more than 

 other areas. If the scales could subserve this function of strength- 

 ening the m-mbrane it is apparent that the flat scale with short, stiff 

 pedicel and broad blade, lying closely against the membrane would 

 be much better fitted to fulfil this function than would the slender, 

 flexible, hair-like form rising weakly from the wing-membrane. The 

 flattened scale would have additional strength, too, from its corrugated 

 condition (shown in fig. 9), as the corrugations would help to prevent 

 bending of the scales; the longitudinal striations also better enable 

 the scale to resist a force tending to bend it at rigl.t angles to its long 

 axis which, from the manner of the scale's insertion on the wing 

 (viz.: with its pedicel directed toward the base of the wing) would be 

 the case during flight. If, also, there were any variance in the scale- 

 development on the wing, that state of development best adapted for 

 strengthening the membrane found anywhere on the wing should be 

 found on the limbal area of the wing. 



That this condition above described as the one among all the 

 forms and kinds of scales observable among Lepidoptera best adapted 

 for the function of adding strength to the membrane does actually 

 obtain on the limbal area an inspection of the wings of Lepidoptera soon 

 demonstrates, while the basal and anal areas present those of all the 

 scales of the wing most widely departing from the type of flat, 

 blade-like form. 



I consider, therefore, the flattened, symmetrical scale, with short, 

 stiff pedicel and broadly expanded, irregularly corrugated and 

 striated blade the more specialized form of scale; while the slender, 

 flexible, hair-like form is the more generalized condition. 



