RESEMBLANCES AMONG ANIMALS. 81 



externally, as if it acquired also the disagreeable odour ; 

 always supposing that there were only a few of them 

 among a great number of the Heliconias. If the birds 

 could not distinguish the two kinds externally, and 

 there were on the average only one eatable among 

 fifty uneatable, they would soon give up seeking for 

 the eatable ones, even if they knew them to exist. If, 

 on the other hand, any particular butterfly of an eatable 

 group acquired the disagreeable taste of the Heliconias 

 while it retained the characteristic form and colouring 

 of its own group, this would be really of no use to it 

 whatever ; for the birds would go on catching it among 

 its eatable allies (compared with which it would rarely 

 occur), it would be wounded and disabled, even if re- 

 jected, and its increase would thus be as effectually 

 checked as if it were devoured. It is important, there- 

 fore, to understand that if any one genus of an extensive 

 family of eatable butterflies were in danger of extermi- 

 nation from insect-eating birds, and if two kinds of 

 variation were going on among them, some individuals 

 possessing a slightly disagreeable taste, others a slight 

 resemblance to the Heliconida?, this latter quality would 

 be much more valuable than the former. The change 

 in flavour would not at all prevent the variety from 

 being captured as before, and it would almost certainly 

 be thoroughly disabled before being rejected. The ap- 

 proach in colour and form to the HeliconidaB, however, 

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

 slight advantage ; for although at short distances this 

 variety would be easily distinguished and devoured, yet 



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