THE WINGS OF LEPIDOPTERA 321 



The development of ridges on the surface of scales adds greatly to their 

 stiffness, and thus increases their efficiency as a protective covering, as the 

 corrugations in the sheets of iron used for covering the sides of buildings 

 adds to the stiffness of the metal. 



Upon the wings a covering of rigid scales would serve not merely to 

 protect the wings but would tend to stiffen them, and thus arose a secondary 

 function of scales which has resulted in the perfecting of their arrangement 

 upon the wings in the more specialized members of the order as already 

 indicated. 



There are great differences among the insects of this order regarding 

 the regularity of the arrangement of the scales upon the wings. With some 

 of the more generalized moths the scales are scattered irregularly over the 

 surface of the wings. But if a wing of one of the more specialized butter- 

 flies be examined with a microscope the scales will be found arranged in 

 regular overlapping rows ; the arrangement being as regular as that of the 

 scales on a fish or of the shingles on a roof. Figure 328 represents a small 

 portion of a wing of one of the more 



specialized butterflies, where the ^--^-jj;;-;^.,;-;;?^;;;:?^^^ 

 arrangement of the scales is most ,;K3;:^^'^^^"'--^v--''^^^^^:^;;^^^ii^ 



perfect. In the upper part of the 

 figure the membrane is represented ^^g- 33i. -Cross-section of soiles^ of Par- 



^ ^ nasstus smtntheus (After Kellogg). 



with the scales removed. 



Even in those insects in which a very perfect arrangement of the scales 

 upon the wings has been attained, great differences in the degree of perfec- 

 tion of this arrangement exists in the tv/o wings of the same side and in the 

 different parts of the same wing. The arrangement is most perfect in those 

 wings and in those parts of each wing that are subjected to the greater 

 strain during flight. And is more perfect in swift flying species that it is 

 in those of slow flight. 



The taxonomic value of these differences in the arrangement of the 

 scales of the wings of the Lepidoptera and also of the different types of 

 scales found in different divisions of the order was investigated by Professor 

 Kellogg ('94), to whose extended account the reader is referred for a dis- 

 cussion of this phase of the subject. 



A secondary use of the scales of the Lepidoptera is that of ornamenta- 

 tion ; for the beautiful colors and markings of these insects arc due entirely 

 to the scales, and are destroyed when the scales are removed. 



The various colors of insects, and of other animals are produced in 

 quite different ways ; and classifications of these colors have been proposed 

 based on the methods of their production. The literature of this subject is 

 too extensive to be referred to in detail here. A most enjoyable, popular 

 account is given by Professor Kellogg in his Aniericaii Insects (Kellogg '08, 

 pp. 583-614) and a detailed analysis of the methods of the production of 



