46 THE COLOURS OF ANIMALS 



Protective Kesemblance, which will be described in 

 Chapters VII., VIII., and IX., the individual can 

 adjust its appearance to any of the various environ- 

 ments it is likely to meet with in nature. 



The consideration of changes in colour very 

 naturally leads to the subject of Dimorphism. 



Dimorphism in Lepidopterous larvae 



It has been already mentioned that the caterpillars 

 of the Large Emerald Moth are sometimes green and 

 sometimes brown. The same is true of many larvae, 

 and in some of the Mocha Moths (Ephyrida;) the 

 chrysalides are the same colour as the larvae from which 

 they develop. These colours have nothing to do with 

 sex, and the appearance of the perfect insect does not 

 seem to be influenced in any way by the larval dimor- 

 phism. It is noteworthy that both colours of dimorphic 

 larvae are invariably of protective value : they are, in 

 fact, nearly always the two chief tints of nature — 

 green and brown. 



If we breed from moths developed from the green 

 larvae of, e.g.^ the Large Emerald, the larvae in the 

 next generation are chiefly green, and after several 

 generations there is little doubt that the brown form 

 would become excessively rare ; so also the green form 

 would disappear if we bred from the brown varieties. 

 But in nature both forms are common, and therefore it 

 is certain that both must be advantageous to the species, 



