Fig. 221.—Flattened and spinulated hairs of tufts of larva of Acronycta hastulifera.
Fig. 222.—Scales from dorsal tuft, on second thoracic segment of larva of Gastropacha quercifolia.
The scales vary much in shape, but are more or less tile-like, attached to the surface of the body or wing by a short slender pedicel, and are more loosely connected with the integument than the hairs, which are thicker at the base or insertion than beyond.
The markings of the scales, both of Synaptera and Lepidoptera, are very elaborate, consisting of raised lines, ridges, or striæ with transverse ridges between. “The striæ of the transparent scales of Micropteryx are from about 500 to 300 to the millimetre, varying in different species. The opaque scales of Morpho, which show metallic reflections, have about 1400 striæ 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 cases (as first claimed by Kettelhoit in 1860) 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 Plusia 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 Trichoptera and of Amphientomum.
Fig. 223.—Portion of a longitudinal section through one of the young pupal wings of a summer pupa of Vanessa antiopa: s, young scale; leu. cy., leucocyte; mbr. pr., ground membrane; prc, hypodermis-cells.