SCALES. 



[ 564 ] 



SCALES. 



obcordate, or cuneate, &c. (Pis. 1 & 27) ; 

 sometimes they are filiform or capillary (PI. 

 27. fig. 27). Their free end is rounded, 

 truncate, toothed, or terminated by a num- 

 ber of hair-like processes ; and they are ar- 

 ranged like the tiles of a roof, overlapping 

 each other (PI. 27. fig. 26). 



The interesting markings seen upon the 

 scales vary considerably in different insects. 

 The most common, as seen by transmitted 

 light, are longitudinal, simple, continuous, 

 parallel or slightly radiating dark striae or 

 lines (PI. 1. figs. 6, 7, 8, 9 a). These are 

 met with upon the scales of nearly all butter- 

 flies, and many other insects. In some in- 

 sects the striae are not simple and continuous, 

 but are made up of rows of smaller striae in 

 twos or threes meeting at an angle (PI. 27. 

 figs. 286, 30 & 31). In others they are 

 composed of a number of bead-like dots, or 

 are interrupted, still preserving their general 

 longitudinal direction (PL 27. fig. 24) ; or 

 they are slightly undulate or irregular, and 

 give off short lateral branches (PI. 27. figs. 

 23 a & 29). In others, again, they present 

 dilatations in certain parts of their course 

 (PL 27. figs. 20 & 21). 



These longitudinal striae consist of eleva- 

 tions or ridges upon the surface, probably 

 representing folds of the upper layer or 

 membrane of the scale. They often project 

 slightly from the free end of the scale (PL 

 27- figs. 3 & 22) ; and, when moistened, 

 bubbles of air may not unfrequently be found 

 imprisoned between the surface of the scale 

 and the cover, which, being confined between 

 two of the ridges, assume an oblong form. 

 They sometimes contain air, which may be 

 displaced by liquid (PL 27. fig. 21). We 

 have never been able to detect tracheae in 

 these folds or in the scales. A minute coni- 

 cal point or spine sometimes occurs in each of 

 the dilatations when present (PL 27. fig. 20 a). 

 In the scales of Podura (PL 1. fig. 12), the 

 striae consist of longitudinal rows of minute 

 wedge-shaped bodies. 



In addition to the longitudinal striae, on 

 most scales, especially when examined by 

 unilateral oblique light, are seen a number 

 of minute transverse striae (PL 1 . figs. 7 & 9 a). 

 These are neither indications of ridges nor 

 depressions, but arise from the existence of a 

 number of pigment-granules situated between 

 the two layers of the scale ; and the appear- 

 ance of striae has the same origin as that in 

 the case of the valves of the Diatomaceae. 

 This point is best examined in brown or 

 other dark-coloured scales. If perfectly direct 



i. e. not oblique) light be transmitted through 

 one of these scales, the transverse striae va- 

 nish, their place being occupied by the di- 

 stinct and isolated granules of pigment (PL 

 1 . fig. 9 &) ; the scale should also be im- 

 mersed in balsam or liquid, to diminish the 

 effects of the refraction arising from the in- 

 equalities of the surface of the scale. On 

 then transmitting unilateral oblique light 

 through the scale, the appearance of trans- 

 verse striae may be easily produced. 



The colours of the scales of insects arise 

 partly from iridescence, partly from the pre- 

 sence of pigment ; in general, the brilliant 

 colours depending upon the former, and the 

 more sombre hues upon the latter. The 

 darkness of the longitudinal striae is caused 

 by refraction, for scales containing no pig- 

 ment appear perfectly white by reflected 

 light, although the striae may be very dark. 

 Upon certain scales, other irregular, more 

 or less transverse curved striae exist (PL 27. 

 figs. 3 & 22); these appear to consist of 

 wrinklings or folds of the under mem- 

 brane of the scale. 



In examining the scales of insects, they 

 should be viewed both in the dry state and 

 immersed in water or oil of turpentine, and 

 both by transmitted and reflected light. 

 When the insects are pressed against the slide 

 to remove the scales, a number of globules 

 of oil adhere simultaneously to the slide ; and 

 when the cover is applied, the scales often 

 become partially or entirely covered with the 

 oily matter, producing an appearance as if the 

 upper layer of the scale were removed, and 

 rendering the markings so pale and indi- 

 stinct, as to be apparently absent. The ap- 

 pearance of transverse striae is best produced 

 by turning the mirror to one side, so as to 

 reflect unilateral light. 



A brief notice of some interesting insects 

 in respect to the structure of their scales is 

 given under the individual heads, as CULEX, 



CURCULIO, MORPHO, LEPISMA, PoDURA, 

 POLYOMMATUS, PONTIA, TlNEA, &C. 



See also TEST-OBJECTS. 



BIBL. Westwood, Introduction, fyc., and 

 British Butterflies ; Deschamps, Ann. desSc. 

 nat. 2 ser. iii. p. Ill; Bowerbank, Entomol. 

 Mag. No. 23. 304 ; Craig, Phil. Mag. 1839. 

 xv. p. 279 ; Dujardin, Obs. au Microscope ; 

 Ratzeburg, Die Forst- Insekten ; Siebold, 

 Vergleich. Anat. 



SCALES, OF PLANTS. Under the head 

 of HAIRS mention has been made of scales 

 (lepides) occurring on the epidermis of 

 plants. They consist of flat, usually more 



