<')56 INSECTS AND AKACHNIDA. 



them from the inner surface, and extend towards the outer with- 

 out reaching it. Occasionally, however, even this exhibits very 

 clear indications of cellular structure ; of which a good example 

 is afforded by the middle layer of the lamellfe of the antenna of 

 the CocJcchaffer (Fig. 286, a), wherein is plainly to be seen an 

 assemblage of rounded cells with large nuclei, lying in the 

 midst of a homogeneous intercellular substance, and thus closely 

 resembling Cartilage (Fig. 324) in structure, though differing 

 from it in chemical composition. 



379. Tegtimentary 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 

 soraetimes being intermediate between the two. The scaly in- 

 vestment 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 dis- 

 tinguished; all the scales of one patch (for example) being green, 

 those of another red, and so on ; for the subjacent membrane re- 

 mains perfectly transparent and colorless, when the scales have 

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

 posed of two superficial colored laminae, enclosing a central 

 lamina of structureless membrane, 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 ar- 

 rangement which may often be discerned in scales that have 

 lost a portion of their superficial layer by some accidental injury 

 (Fig. 281, c). The color of the superficial laminae seems to be 

 generally inherent in their substance, especially in the Lepidop- 

 tera ; 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 colors 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. 279-281), by which it is fitte4 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 magni- 

 fied, very much the appearance of being tiled like the roof of a 

 house. Such an arrangement is said to be "imbricated." The 

 foi'ms 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 for- 

 mer, and narrower and more hair-like on the latter. The 



