78 ENTOMOLOGY 
posed, surface of the scale (Fig. 93) and number from 
33 or less (dnosia) to 1,400 (Morpho) to each scale, the 
strie being from .002 mm. 
Fic. 94. 
to .0007 mm. apart (Kel- 
loge); between these longi- 
tudinal ridges may be dis- 
cerned delicate transverse 
markings. Internally, scales 
are hollow and often contain 
pigments derived from the 
blood. 
On the wing of a butter- 
fly the scales are arranged 
in regular rows and overlap 
one another, as in Fig. 04; 
in the more primitive moths 
and in Trichoptera, how- 
Arrangement of scales on the wing of a ever, their distribution 1s 
butterfly, Papilio. ; 
rather irregular. 
A scale is the equivalent of a hair, for (1) a complete series 
of transitions from hairs to scales may be found on a single 
individual (Fig. 95); and (2) hairs and scales agree in their 
manner of development, as shown by Semper, Schaffer, Spu- 
PIGwOs: 
/ *\ 
l \ \f y hu M4 
V 
Hairs and scales of a moth, Samia cecropia. 
ler, Mayer and others. Both hairs and scales arise as pro- 
cesses from enlarged hypodermis cells, or formative cells (Vig. 
96). The scale at first contains protoplasm, which gradually 
withdraws, leaving short chitinous strands to hold the two 
membranes of the scale together. 
