322 Studies in the Theory, of Descent. 



but always in the deep shadow of the leaves, in 

 which situation the coloured edges produce their 

 peculiar effect. It may be objected that the 

 oblique white stripes, standing simply on a dark- 

 green ground-colour, would produce the same 

 effect, and that my explanation therefore leaves 

 the bright colouring of these edges still unaccounted 

 for. I certainly cannot say why in Sphinx 

 Ligustri these edges are lilac, and in ,5*. Drupife- 

 rarum, S. Print, and Dolba Hylceus red, nor why 

 they are black and green in Macrosila Rustica, and 

 blue in Acherontia Atropos. If we knew exactly 

 on what plants these caterpillars fed originally, we 

 might perhaps indulge in comparing with an 

 artistic eye the shadows playing about their 

 leaves, seeing in one case more red, and in an- 

 other more blue or violet. The coloured stripes 

 of the Sphingidce must be regarded as the 

 single strokes of a great master on the countenance 

 of a human portrait. Looked into closely, we 

 see red, blue, or even green spots and strokes ; 

 but all these colours, conspicuous when close, dis- 

 appear on retreating, a general effect of colour 

 being then produced, which cannot be precisely 

 described by words. 



Quite in accordance with this explanation, we 

 see caterpillars with the brightest coloured stripes 

 concealing themselves in the earth by day, and 

 betaking themselves to their food-plants only in 

 the dusk of the evening or dawn of morning and 



