TEGUMENTAKY APPENDAGES OF INSECTS : — SCALES. 655 



guishable when the light is reflected from it at a particular angle, 

 even when not discernible in transparent sections. The integument 

 of the common Red Ant exhibits the hexagonal cellular arrange- 

 ment very distinctly throughout ; and the broad flat expansion of 

 the leg of the Crahro (Sand-wasp) affords another beautiful example 

 of a distinctly-cellular structure in the outer layer of the integu- 

 ment. The inner layer, however, which constitutes the principal 

 part of the thickness of the horny casing of the Beetle -tribe, seldom 

 exhibits any distinct organization ; though it may be usually sepa- 

 rated into several lamina?, which are sometimes traversed by tubes 

 that pass into them from the inner surface, and extend towards the 

 outer without reaching it. 



512. Tegumentai'y Appendages. — The surface of many Insects 

 is beset, and is sometimes completely covered, with appendages, 

 having sometimes the form of broad flat Scales, sometimes that of 

 Hairs more or less approaching the cylindrical shape, and some- 

 times being intermediate between 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 

 of 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 superficial 

 coloured laminae, enclosing a central lamina of structureless mem- 

 brane, the surface of which is highly polished, and which acts as a 

 ' foil' to increase their brilliancy by reflecting back the light that 

 passes through them, — an arrangement which may often be dis- 

 cerned in Scales that have lost a portion of their superficial layer by 

 some accidental injury.* The colour of the superficial laminae 

 seems to be generally inherent in their substance, especially in the 

 Lepidoptera; but it sometimes appears to be (like the prismatic 

 hues of a soap-bubble) a purely -optical effect of their extreme 

 thinness, this being especially the case among those Beetles, as the 

 Curculio imperialis (Diamond-beetle), the Scales of which have a 

 metallic lustre, and exhibit colours that vary with the mode in 

 which the light glances from them. Each Scale is furnished with 

 a sort of handle at one end (Figs. 334, 335), by which it is fitted 

 into a minute socket attached to the surface of the insect ; and on 

 the Wings of Lepidoptera 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, 



* See the Memoir of M. Bern. Deschamps 'Sur reorganisation des ailes 

 de Lepidopteres,' in '« Ann. des Sci. Nat.," Ser. 2, Zool., Tom. iii. (1835), 

 p. 111. 



