56 
NATURAL SELECTION 
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remarkable. They are so abundant and characteristic in 
all the woody portions of the American tropics, that in 
almost every locality they will be seen more frequently than 
any other butterflies. They are distinguished by very elon- 
gate wings, body, and antennae, and are exceedingly beautiful 
and varied in their colours ; spots and patches of yellow, red, 
or pure white upon a black, blue, or brown ground being 
most general. They frequent the forests chiefly, and all fly 
slowly and weakly ; yet although they are so conspicuous, 
and could certainly be caught by insectivorous birds more 
easily than almost any other insects, their great abundance 
all over the wide region they inhabit shows that they are not 
so persecuted. It is to be especially remarked also, that they 
possess no adaptive colouring to protect them during repose, 
for the under side of their wings presents the same, or at least 
an equally conspicuous colouring as the upper side ; and they 
may be observed after sunset suspended at the end of twigs 
and leaves, where they have taken up their station for the 
night, fully exposed to the attacks of enemies if they have 
any. These beautiful insects possess, however, a strong 
pungent semi-aromatic or medicinal odour, which seems to 
pervade all the juices of their system. When the entomolo- 
gist squeezes the breast of one of them between his fingers to 
kill it, a yellow liquid exudes which stains the skin, and the 
smell of which can only be got rid of by time and repeated 
washings. Here we have probably the cause of their im- 
munity from attack, since there is a great deal of evidence to 
show that certain insects are so disgusting to birds that they 
will under no circumstances touch them. Mr. Stainton has 
observed that a brood of young turkeys greedily devoured all 
the worthless moths he had amassed in a night’s “ sugaring,” 
yet one after another seized and rejected a single white moth 
which happened to be among them. Young pheasants and 
partridges which eat many kinds of caterpillars seem to have 
an absolute dread of that of the common currant moth, which 
they will never touch, and tomtits as well as other small birds 
appear never to eat the same species. In the case of the 
Heliconidse, however, we have some direct evidence to the 
same effect. In the Brazilian forests there are great numbers 
of insectivorous birds — as jacamars, trogons, and puffbirds — 
