42 THE BUTTERFLIES OF NEW ENGLAND. 



and finely toothed at the apical margin, and at the l)ase constricted into a 

 pedicel with an extreme bulbous expansion by which they are held in place 

 in pockets in the membrane of the wing. The pockets being regularly 

 distributed, the scales are arranged in rows, very much as the slates upon 

 the roof of a house, those of one row^ alternating with those of its neighl^ors 

 and the base hidden from view and specially guarded. It is through the 

 coloring of these scales that all the wonderful variety of the markings upon 

 the wings of butterflies is produced. Many studies of the scales have been 

 made, and their essential identity with hairs clearly established. Every 

 gradation between the two may be found, and those in different parts of 

 the wings often assume special forms. 



In the male sex the variety in the form of scales is often far greater than 

 in the female (46-51). For, certain scales of peculiar form, and in some 

 cases at least serving as outlets to scent-glands, may be found either scat- 

 tered irregularly over portions of the wings or clustered into definite areas. 

 In many cases, especially where it is certain that they are the vehicle for 

 the diffusion of odors from glands, they are attenuated and very delicately 

 fringed, and each microscopic filament of the fringe is a tul)ular canal con- 

 necting with ducts in the membrane of the scale itself to the base Avhere 

 the glands are situated. As the various forms which these scales may 

 assume will be specially treated in the body of this work, and their posi- 

 tion in different groups directly specified, it will be unnecessary here to 

 enter into further details, but a further word may be added regarding the 

 structure of scales in general. 



In general scales may be said to be nothing more than modified hairs. 

 They originate in precisely the same manner and have the same histological 

 structure. As already said, they may be called flattened sacs, being made 

 of two tunics with a hollow interior, forming in fact a closed bag. Origi- 

 nating in a somewhat bladder-like form, the contraction of the upper surface 

 as they become flattened tends to render this surface striate, and the larger 

 striations which are readily seen upon the surface of all scales is confined, 

 as is shown in the cross section at PI. 61 : fig. 38, to the upper surface only. 

 Some scales contain no coloring matter, but they always include some 

 amount of air. As Dimmock has pointed out, the ordinary scales of Pieris 

 rapae and the metallic silvery scales of the spots on the under surface of the 

 fritillaries contain no appreciable coloring matter and both contain air ; and 

 he believes that, as in a common mirror the mercuiy amalgam serves to 

 give a silvery reflection, so the layer of air cavities in the interior of these 

 scales answers the same purpose, the colors being only optical effects pro- 

 duced by reflected light. But in most scales, there is plainly a pigment 

 enclosed between the two layers of which the scale is composed, sealed up 

 as it were for better protection against the action of the air, and which, ac- 

 cording to Burmeister, is principally attached to the upper layer of the 



