ENTOMOLOGY 



FIG. 94- 



Arrangement of scale's on the 

 butterfly, Papilio. 



posed, surface of the scale (Fig. 93) and number from 

 33 or less (Anosia) to 1,400 (Morpho) to each scale, the 



striae being from .002 mm. 

 to .0007 mm. apart (Kel- 

 logg) ; 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. 94; 

 in the more primitive moths 

 and in Trichoptera, how- 

 n g of a ever, their distribution is 



rather irregular. 

 A scale is the equivalent of a hair, for ( i ) 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- 



FIG. 95- 



\u 



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 (Fig. 

 96). The scale at first contains protoplasm, which gradually 

 withdraws, leaving short chitinous strands to hold the two 

 membranes of the scale together. 



