162 THE COLORING OF BUTTERFLIES, 



phenomenon, the appearance of those varieties 

 or sports which are called examples of suffusion. 

 Although they frequently seem very unlike the 

 normal form, a little study always suffices to 

 show to what species they belong. This disguise 

 is produced by the blending of certain colors, 

 especially of black, white, or silvery tints, which 

 normally occur at distinct parts of the wing ; 

 there may be, for example, two parallel series of 

 white spots normally crossing the wing in the 

 middle and near the border ; under this disguise 

 of suffusion, the whole intervening area is covered 

 or shot with this color, generally more or less 

 sprinkled with atoms of the normal ground, pro- 

 ducing an impure tint, characteristic of north- 

 ern countries. Now these suffusions have been 

 known almost exclusively from the temperate 

 regions,* and to show that they are not exces- 

 sively rare, I may add that I have seen nearly 

 fifty specimens of our common American Copper, 

 and we are acquainted with at least eighteen of 

 the two hundred and seven butterflies of the east- 

 ern United States in which such suffusions occur. 

 A large number have been recorded in Europe, 

 where they are commonest in the alpine districts 

 of Switzerland. 



These general changes of prevailing tints among 



* Mr. Edwards of West Virginia has artificially produced a 

 number of instances by subjecting chrysalids to unusual cold. 



