BUTTERFLY-HUNTING BEGINS. 35 



colour betrays them get thinned out by their 

 watchful enemies, while those whose colour 

 protects them manage to lay their eggs in 

 peace, and hand on their own peculiar spots 

 and lines to their descendants. The con- 

 sequence in the long run is that the butterflies 

 get better protected from generation to 

 generation, as the chances of interbreeding 

 with badly protected individuals are 

 eliminated by the action of the birds, while 

 only the most imitatively coloured individuals 

 are left to mate with one another and to 

 become the parents of future swarms. Thus 

 the hostile birds are themselves the instru- 

 ments through which the insects have been 

 armed defensively against their depredations. 

 For the various individuals tend always to 

 vary a little in marking no two plants or 

 animals of the same species are ever exactly 

 alike but the picking off of the brightly 

 coloured individuals by the birds helps to 

 preserve the protected specific type intact. 

 And of course the same causes which now 



D 2 



