PROTECTIVB MIMICRY. 207 



An objection which strikes at the root of the whole matter 

 has been combated by Mr. Belt. I quote the passage which 

 relates to the matter in full : — 



" The extraordinary jjerfection of these mimetic resemblances 

 is most wonderful. I have heard this urged as a reason for 

 believing that they could not have been produced by natural 

 selection, because a much less degree of resemblance would 

 have protected the mimetic s})ecies. To this it may he 

 answered that natural selection not only tends to pick out 

 and preserve the forms that have protective resemblances, 

 but to increase the perce])tions of the predator}- species of 

 insects and birds, so that there is a continual progression 

 towards a perfectly mimetic form. This progressive improve- 

 ment in means of defence and attack may be illustrated in this 

 way. Suppose a number of not very swift hares and a number 

 of slow-running dogs were placed on an island where there 

 was plenty of food for the hares but none for the dogs, except 

 the hares they could catch, the slowest of the hares would be 

 first killed, the swifter preserved ; then the slowest-vnnning 

 dogs would suffei', and, having less food than the fleeter ones, 

 would have least chance of living, and the swiftest dogs would 

 be preserved : thus the fleetness of both dogs and liares would 

 be gradually but surely perfected by natural selection, until 

 the greatest sjjeed was reached that it was possible for them 

 to attain. I have in this snpjiosed example limited myself to 

 the ipiestion of speed alone: but, in reality, other means of 

 pursuit and escape would come into play and be imi>roved. 

 The dogs might increase in cunning, or combine together to 

 work in couples or in packs by the same selective process ; 

 and the hares, on their part, might acquire means of conceal- 

 ment or stratagem to elude their enemies ; but, on both sides, 

 the improvement would be progressive until the highest form 



