Vlll INTRODUCTION. 



sides of Spilosoma menthastri, which becomes quite yellow in North 

 British and Irish localities, although this particular form is compara- 

 tively rare in the South of England. This is really parallel to the 

 intensification of colour in the undersides of butterflies, when we con- 

 sider that the latter use their undersides for protective purposes and not 

 the uppersides as in the genus Spilosoma. The undersides in Melanargia 

 galatea are, as I have before mentioned, often strongly yellow, and it 

 is strange that whilst the females of M. galatea are whitest (oldest 

 form) on the uppersides, and the males more ochreous (more highly 

 developed) ; yet, on the undersides, when it is necessary for the female 

 to be more protected to perpetuate its species, the colouring is more 

 intense than in the male, thus proving conclusively that in this instance 

 the ochreous coloration is an advantage, and that although the males 

 have broadly adapted themselves more readily to the change, the 

 females, whilst retaining their original colour on the upper side, have 

 adopted the advantageous colour on the lower. Yellow, therefore, in 

 nature, appears to be a direct derivative from white, and when yellow 

 or orange varieties of a white species occur, I look on them generally 

 as progressive forms, whilst white varieties of normally yellow species 

 are generally retrogressive forms. Of these latter forms Urapteryx 

 sambucata var. persica, Nemeophila plantaginis var. hospita, the white 

 form of Bumia cratcegata, Triphcena orbona var. pallescens, Heliodes 

 arbtiti var. albescens are good examples. Two strange phenomena 

 occur in Lithosia mesometta and L. caniola. In the former species two 

 distinct types of coloration, white and yellow, exist side by side and 

 are equally common, the yellow being probably a progressive form of 

 the white, whilst L. caniola has a variety lacteola with the anterior 

 wings white, probably the white in this var. must be looked upon as 

 retrogressive, as must the var. helice of Colias edusa. 



We must now consider the progressive development of yellow. 

 As pigmented yellow coloration has been shown to be the more or less 

 direct derivative of a white pigmented coloration, so we must look 

 upon red and all its different forms, brown &c., as more or less direct 

 derivatives of yellow. Pigmented yellow, however, may be of many 

 various shades and tints, and extend from the pale hue of female 

 Gonopteryx rliamni to the deep orange of Colias edusa and Angerona 

 prunaria. Now although the transition, in nature, from yellow or 

 orange to red is not particularly common, it very frequently occurs. 

 In the year 1887, many of the Colias edusa captured, had distinct red 

 shades, Arctia villica var. fidminans has the posterior wings red, 

 Sfrilosoma menthastri ab. luxerii has the anterior wings rosy, whilst 

 occasionally S. lubricipeda is so tinted. It is not difficult to trace 

 Cirrhcedia xerampelina from pale yellow to deep orange-red and purple, 

 Xanthia cerago (fidvago) is also traceable from the palest yellow to the 

 deepest orange with a large quantity of red marks, whilst the bright 

 red of F. urticce is essentially orange in its character as may be seen by 

 careful examination of a considerable number. The numerous Lenca- 

 nidce, L. impura, L. pattens, Tapinostola hellmanni, Calamia lutosa, C. 

 phragmitidis, Nonagria cannce, N. fulva and many others, show the 

 progressive tendency from ochreous to red, and there are other 

 examples too numerous to mention. The retrogressive change of 

 brown or red to yellow, however, is much more common ; some 

 examples of this will be mentioned later. 



