34 THE GENESIS OF SPECIES. [CHAP. 



semblance Mr. Wallace observes : l " Tropical insectivorous 

 birds very frequently sit on dead branches of a lofty tree, 

 or on those which overhang forest paths, gazing intently 

 around, and darting off at intervals to seize an insect at a 

 considerable distance, with which they generally return to 

 their station to devour. If a bird began by capturing the 

 slow-flying conspicuous Heliconidse, and found them always 

 so disagreeable that it could not eat them, it would after a 

 very few trials leave off catching them at all ; and their 

 whole appearance, form, colouring, and mode of flight is so 

 peculiar, that there can be little doubt birds would soon 

 learn to distinguish them at a long distance, and never 

 waste any time in pursuit of them. Under these circum- 

 stances, it is evident that any other butterfly of a group 

 which birds were accustomed to devour, would be almost 

 equally well protected by closely resembling a Heliconia 

 externally, as if it acquired also the disagreeable odour ; 

 always supposing that there were only a few of them 

 among a great number of Heliconias. 



" The approach in colour and form to the Heliconidae, 

 however, would be at the first a positive, though perhaps 

 a slight, advantage ; for although at short distances this 

 variety would be easily distinguished and devoured, yet at 

 a longer distance it might be mistaken for one of the 

 uneatable group, and so be passed by and gain another 

 day's life, which might in many cases be sufficient for it 

 to lay a quantity of eggs and leave a numerous progeny, 

 many of which would inherit the peculiarity which had 

 been the safeguard of their parent." 



As a complete example of mimicry Mr. Wallace refers 

 to a common Indian butterfly. He says : 2 " But the 



1 Loc. cit. p. 80. 2 Ibid. p. 59. 



