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 Heliconide, 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 Heliconide, 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 
G 
