108 ANIMAL COLORATION. 



Colour will be fonud to be due to chlorophyll existing in the 

 internal tissues of the stems of that plant. 



I have already referred to this subject in connection with 

 the direct influence of light upon colour. 



Comparative Rarity of Green tree-frequenting Animals an Argument 



in favour of Selection. 



It is not a little surprising to find how few green animals 

 there are : this assertion may appear to be rather bold ; but if 

 we consider the great prevalence of sandy coloured animals in 

 arid and sandy localities, the absence of a correspondingly large 

 number of green animals among trees is striking. As regards 

 birds, we cannot fairly take this country as an example, be- 

 cause, as Mr. Wallace has pointed out, the deciduous foliage 

 would expose green-coloured birds in the winter and in the 

 early spring, when they most need protection; but insects, 

 which only survive for a summer, may be fairly taken as a 

 crucial test. There is only one butterfly the green Hair- 

 streak (Tlteda rali} which is distinctly green; the mottling 

 or veining of green on the under surface of the wings in the 

 Pieridte is supposed to be a special adaptation to a particular 

 plant.* Among moths the number of green species is not 

 proportionately much greater, there are eight species of Emerald 

 moths, which are all of a nearly uniform green colour; four or 

 five Tortrices with the upper wings green ; and a few Noctua3 

 in which green forms a large component part of the coloration in 

 the upper wings at least; finally, we have the two "Forester" 

 moths. Green Lepidoptera do not appear to be relatively 

 more abundant in tropical countries. There are plenty of 

 green beetles ; but on turning over the plates which illustrate 



* Mr. T. W. Wood has figured (' Student,"' vol. ii.) the orange-tip at rest 

 upon an umbelliferous plant, to which its speckled green under- wings 

 bear a striking resemblance. See Woodcut, fig. B, p. H7. 



