56 Kansas universitv quarterly. 



It is evident also that a regular arrangement of the scales in 

 transverse rows, with the scales of one row overlapping those of the row 

 in front and with the scales in each row overlapping by their lateral 

 margins, as described and illustrated on pages 47 and 48, figures 2, 3 

 and 4, producing an evenly disposed covering or sheath of scales over 

 the membrane, would better subserve the function of strengthening the 

 wing-membrane than would a condition of arrangement whereby the 

 scales were irregularly scattered over the wing-surface. Even though the 

 scales might be numerous enough in this condition to form a fairly 

 complete covering over the membrane, its strength would be uneven, 

 and its adaptation for its function inferior to the more regular 

 arrangement. An inspection of any wing shows that the nearest 

 approach to a regular arrangement of the scales in rows and tiers to 

 be met with anywhere on the wing is to be found on the limbal area, 

 where the necessity for a strengthening of the membrane is most 

 urgent. 



A regular and uniform scale-arrangement may therefore be con- 

 sidered to be a more highly specialized condition than an irregular 

 arrangement of the scales. 



Confirmation of what the function and specialized form of the 

 scales are is offered by a further examination of the wings, while 

 having in mind the use of the wings in flight. In addition to the 

 correlation just cited between the specialization of scales and scale-ar- 

 rangement of the limbal area of the wing and that area's special need in 

 flight, it is apparent that the costal area of the wing plays a more 

 important part in flight than the anal area; a comparison of the scale- 

 covering shows a higher specialization of scale-form and arrangement 

 in the costal than in the anal area. Again, as the tendency in Lepi- 

 doptera is towards a cephalization of flight, the forewings are much 

 more important in flight than the hindvvings. A comparison of the 

 covering of the fore and hindwings usually (uniformly, where con- 

 siderable cephalization of flight has been attained) shows that the 

 scale-forms and arrangement of the forewings much more nearly 

 approach those specialized conditions previously described than do 

 the scale-forms and arrangement of the hindwings. And, finally, 

 offering a general character of some taxonomic importance, the scale- 

 specialization is higher in moths (for the time being I exclude butter- 

 flies from consideration, as explained later) of highly-specialized 

 flight-function (indicated by cephalization of flight) than in moths of 

 more generalized flight-function, as, for example, the Sphingidae 

 compared with the Saturniidse. But the hind wings of moths where 

 an extreme cephalization of flight has been arrived at, show a less 

 specialization of the scale-covering than is shown by the hind wings 



