'USE OF THE SCALES 



195 



opaque scales of Morpho, which show metallic reflections, have 

 about 1400 striae to the millimetre." (Kellogg.) 



The primary use of scales, as observed by Kellogg, is to protect 

 the body, as seen in. Synaptera and Lepidoptera. A nearly as 

 important use is the production of colors and patterns of colors and 

 markings, while in certain butterflies certain scales function as the 

 external openings of dermal scent-glands, and they afford in some 

 case's (as first claimed by Kettelhoit in I860) generic and specific 

 characters. Spuler has shown that the scales are strengthened by 

 internal chitinous pillars. Burgess has observed in the scales of 

 Danais plexippus that the under surface of the scales is usually 

 smooth, or provided with few and poorly developed ridges, and this 

 has been confirmed by Spuler and by Mayer (Fig. 226). 



In the irised and metallic scales the ridges, says Spuler, are not 

 divided into teeth, and they converge at the base to the pedicel and 

 also toward the end of the scale (Micropteryx), or end in a single 

 process beyond the middle (the brass-colored scales of Phisia chrysitis). 



The arrangement of the scales on the wings is, in the generalized 

 moths, irregular ; in the more specialized forms they are arranged 

 in bands forming groups, and in the most specialized Lepidoptera 

 they are more thickly crowded, overlapping each other and inserted 

 in regular rows crossing the wings, these rows either uniting with 

 each other or running parallel. (Spuler.) The scattered irregular 

 arrangement seen in Micropteryx is also characteristic of the Tri- 

 choptera and of Amphientomum. 



Development of the scales. - - The mode of origin of the scales was 

 first worked out by Semper in 1886, who stated that in the wing of 

 the pupal Sphinx and Saturnia they are seen, in sections, to arise 



prc. 



Fi. 223. Portion of a longitudinal section 

 throiii, r h Mm- of thf younir pupal wings of a sum- 

 mer pupa of I'niit'tstHt (Hif/njiii : s, young scale; 

 leu. c//., leucocyte : iiil>i . jir., ground membrane ; 

 J>rc, liyitoclermis-cells. 



brpr 



FIG. 224. Portion of a longitudinal 

 section through one wall only of the 

 pupal wing of a specimen slightly older 

 than that of Fig. 2'2M ; .v, older scale. 



from large roundish cells just under the hypodermis and which 

 have a projection which passes out between the hypodermis (his 

 " epidermis ") cells, expanding into a more or less spherical vesicle, 

 the latter being the first indication of the future scale. He 



