PASSIVE VARIATIONS. 1 89 



Helices for example the variations amongst some species 

 are so diverse, the banding and colouring so variegated and 

 manifold, that occurring in many groups of animals such 

 wide superficial differences would be classed as separate 

 species, and even as distinct genera. 



So long however as variations in an animal do not 

 produce any disadvantage, so long, in fact, as they are 

 merely passive, they may persist and continue to an almost 

 indefinite extent. 



But even when a species has varied in such a manner 

 and to such an extent that it seems to have acquired, so 

 far as is possible, complete protection from its enemies and 

 to be exactly adapted to its surroundings and mode of 

 living, variations do not cease to take place. 



That this is the case is shewn in one of the most 

 remarkable of known instances of protective resemblance 

 to natural surroundings ; that of the " leaf butterflies." In 

 the Kallimce, and many other genera of the Lepidoptera the 

 resemblance of the wings to leaves when the insects are at 

 rest is so great as to deceive the most practised and 

 critical eye. (Fig. 4.) But although the simulation is so 

 close and the likeness so near, and although all have the 

 appearance, marking and colours of decaying and dead 

 leaves the divergence in the individual is very considerable. 

 "The colour" says Mr. A. R. Wallace writing of the 

 Kallimcs " is very remarkable for its extreme amount of 

 variability : from deep reddish green to olive and pale 

 yellow, hardly two specimens being exactly alike but all 

 coming within the range of leaves in various stages of 

 decay." 



This divergence in the Lepidoptera is not confined to 

 the KalliuicB. In the Doleschallice, AncBincB, and in other 

 cases where protection is secured through resemblance to 

 environment, and the animal is hidden from its enemies 



