3io Studies in the Theory of Descent. 



only in the small group of the Sphingidce but in 

 the whole order Lepidoptera, we shall arrive at 

 the following results : 



i. Complete absence of marking, so common m 

 the larvae of other insects, such as the Coleoptera, 

 is but seldom found among Lepidopterous cater- 

 pillars. 



To this category belong all the species of Sesiidcz 

 (the genera Sesza, Trochilia, Sciapteron, Bembecia, 

 &c.), the larvae of which, without exception, are of 

 a whitish or yellowish colour, and live partly in the 

 wood of trees and shrubs and partly in the shoots 

 of herbaceous plants. Subterranean larvae also, 

 living at the roots of plants, such as Hepialus 

 Humuli at the roots of hop, and H. Lupulinus at 

 those of Triticum Repens, possess neither colour 

 nor marking. These, like the foregoing, are 

 yellowish-white, evidently because they are de- 

 prived of the influence of light. 2 The larvae of 



1 [I have already given reasons for suspecting that the colour 

 of green caterpillars may be due to the presence of chlorophyll 

 (or some derivative thereof) in their tissues (see Proc. Zoo. 

 Soc. 1873, p. 159). This substance appears to be one of great 

 chemical stability, and, according to Chautard, who has detected 

 it in an unaltered state in the tissues of certain leaf-feeding 

 insects by means of its absorption spectrum (" Comp. Rend." 

 Jan. 1 3th, 1873), it resists the animal digestive processes 

 (Ann. Ch. Phys. [5], hi., i 56). If this view should be 

 established by future observations, we must regard the green 

 colour of caterpillars as having been produced, when protective, 

 from phytophagic variability by the action of natural selection ; 

 and the absence of colour in internal feeders, above referred to, 



