40 CHANGE 



effects in spreading it would be still more power- 

 ful they might, indeed, cause it to arise inde- 

 pendently in several individuals. This would 

 explain the curious rigidity with which many 

 species of plants and animals are localized within 

 particular sometimes quite small areas. We 

 may be unable to trace, or to imagine, a connection 

 between the circumstances of a place and some 

 spots on a bird's or a butterfly's wing. But our 

 ignorance, or incapacity, does not entitle us to 

 deny the possibility of its existence. Within recent 

 times a dark variety of the peppered moth (Am- 

 phydasis betularia), formerly very rare, has spread 

 very greatly in the " black country " of the north 

 of England. It seems probable that there are 

 local conditions which favour it. 



To suppose that variations have been spread by 

 imitation may appear to be altogether fantastic. It 

 recalls the success of Jacob in breeding ring-straked 

 sheep ; the story appears incredible, but not a few 

 practical breeders believe that the colour of a 

 calf may be affected by the colour of the cow's 

 stall companion. Nature abounds with illustra- 

 tions of mimicry, and we must not hastily con- 

 clude that an impulse to imitate could not work 

 subconsciously, or that it could not disturb the 

 tendency of the reproductive cells simply to 

 repeat the growth of the preceding generation. 

 Butterflies mimic other butterflies, even dead 

 leaves, and are themselves mimicked by moths ; 

 caterpillars and other insects mimic twigs and 

 foliage ; there is a great] tendency for creatures 

 to take the colour of their environment ; we 

 subconsciously mimic peculiarities of manner in 

 our 1 companions ; families that migrate to a new 



1 One of the most effectively deceptive mimicries is that of a 

 humble-bee (Bombus agrorum) by a fly (Volucella bombylus). 

 These insects inhabit the same nest. 



