INTEGUMENT 975 



either the form of broad flat scales or that of hairs more or less 

 approaching the cylindrical shape, or some form intermediate be- 

 tween the two. The scaly investment is most complete among the 

 Lepidoptera (butterfly and moth tribe), the distinguishing character 

 of the insects of this order being derived from the presence of a 

 regular layer of scales upon each side of their large membranous 

 wings. It is to the peculiar coloration of the scales that the various 

 hues and figures are due, by which these wings are so commonly 

 distinguished, all the scales on one patch (for example) being green, 

 those of another red. and so on ; for the subjacent membrane 

 remains perfectly transparent and colourless when the scales have 

 been brushed off from its surface. Each scale seems to be composed 

 of two or more membranous lamella-, often with an intervening 



O 



deposit of pigment, on which, especially in Lepidoptera, their colour 

 depends. Certain scales, however, especially in the beetle tribe, 

 have a metallic lustre, and exhibit brilliant colours that vary with 

 the mode in which the light glances from them : and this irides- 

 cence,' which is specially noteworthy in the scales of the Curculio 

 imperialis ('diamond beetle'), seems to be a purely optical effect, 

 depending either (like the prismatic hues of a soap-bubble) on the 

 extreme thinness of the membranous lamellae, or (like those of 

 ' mother-of-pearl ') on a lineation of surface produced by their corru- 

 gation. Each scale is furnished at one end with a sort of handle or 

 ' pedicle' (figs. 723, 724), by which it is fitted into a minute socket 

 attached to the surface of the insect ; and on the wings of Lepido- 

 ptera these sockets are so arranged that the scales lie in very regular 

 rows, each row overlapping a portion of the next, so as to give to 

 their surface, when sufficiently magnified, very much the appearance 

 of being tiled like the roof of a house. .Such an arrangement is said 

 to be ' imbricated.' The forms of these scales are often very curious, 

 and frequently differ a good deal on the several parts of the wings 

 and of the body of the same individual, being usually more expanded 

 on the former and narrower and more hairlik'e on the latter. A 

 peculiar type of scale, which has been distinguished by the designa- 

 tion plumule, is met with among the Pieridw, one of the principal 

 families of the diurnal Lepidoptera. The 'plumules' are not flat, 

 but cylindrical or bellows-shaped, and are hollow; they arc attached 

 to the wing by a bulb at the end of a thin elastic peduncle that 

 differs in length in different species, and proceeds from the broader. 

 not from the narrower end of the scale ; whilst the free extremity 

 usually tapers off and ends in a kind of brush, though sometimes it 

 is broad and has its edge fringed with minute filaments. These 

 'plumules,' which are peculiar to the males, are found on the upper 

 surface of the wings, partly between and partly under the ordinary 

 scales. They seem to be represented among the Li/crf/ndc' by the 

 ' battledore' scales to be presently described. 1 



The peculiar markings exhibited by many of the scales very early 

 attracted the attention of opticians engaged in the application of 



1 See Mr. Watson's memoirs ' On the Scales of Battledore Butterflies,' in Monthly 

 Microscopical Journal, ii. pp. 73, 814. 



