ANATOMY AND PHYSIOLOGY 



79 



Uses of Scales. Among Thysanura and Collembola, scales 

 occur only on such species as live in comparatively dry situa- 

 tions, from which it may be inferred that the scales serve to 

 retard the evaporation of moisture through the delicate integu- 

 ment of these insects. This inference is supported by the fact 



FIG. 96. 



FIG. 97. 



Development of butterfly scales. 

 A, Vanessa; B, Anosia. b, base- 

 ment membrane; f, formative cell; 

 h, hypodermis; s, scale. After 

 MAYER. 



Androconia of butter- 

 flies. A, Pieris rapce; B, 

 Everes comyntas. 



that none of the scaleless Collembola can live long in a dry 

 atmosphere; they soon shrivel and die even 'under conditions 

 of dryness which the scaled species are able to withstand. In 

 Lepidoptera the scales are possibly of some value as a mechan- 

 ical protection; they have no influence upon flight, as Mayer 

 has proved, and appear to be useful chiefly as a basis for the 



