140 THE DARWINIAN THEORY 



Among birds, the Cuckoo is undoubtedly protected 

 by its similarity to a hawk in appearance and in 

 mode of flight. In the snakes, again, the harmless 

 ones are said to mimic the venomous. 



The conditions necessary in order to effect 

 mimicry are given by Wallace as follows : — 



(i) The two species, the imitating and the imitated, 

 must occur in the same locality. 



(2) The imitating species must be the more 

 defenceless. 



(3) The imitating species must be less numerous 

 than the imitated, in individuals. 



(4) The imitating species must differ from the 

 bulk of its allies. 



(5) The imitation, however minute, is external 

 only, never extending to internal characters or to 

 such as do not affect external appearance. 



The mode of acquisition of mimicry is by the 

 gradual action of natural selection, and must have 

 been accidental in the first instance. 



Recognition Markings. 



These are closely allied to warning colours, and 

 their purpose is to facilitate recognition, not by 

 enemies, but by friends. They are seen especially 

 in gregarious animals, and specific markings and 

 colours are very probably in many cases not pro- 

 tective, but for recognition. A good instance of this 

 class of colouring is seen in the upturned white tail 

 of the Rabbit, which, although making it conspicuous 

 to its enemies as well as friends, is probably a 



