464 The Journal 
regarded as their ancestral pattern and 
had come to resemble very closely the 
far more abundant Ithomiines among 
whom they habitually flew. To use 
Bates’ term they ‘mimicked’ the Itho- 
miines, and he set to work to devise an 
explanation of how this could have come 
about. The “Origin of Species’’ had 
just appeared and it was natural that 
Bates should seek to interpret this 
peculiar phenomenon on the lines there 
laid down. How was it that these 
Pierines had come to depart so widely 
from the general form of the great bulk 
of their relations, and to mimic so 
closely in appearance species belonging 
to an entirely different group, while at 
the same time conserving the more 
deep-seated anatomical features of their 
own family? 
USEFULNESS OF CHANGE 
“If the change was to be regarded 
as having come about through the 
agency of natural selection it must 
clearly be of advantage to the mimicking 
forms; otherwise natural selection could 
not come into operation. What advant- 
age then have the Ithomiines over the 
majority of butterflies in those parts? 
They are small insects, rather flimsy in 
build, with comparatively weak powers 
of flight, and yet so conspicuously 
colored that they can hardly be mis- 
taken for anything else In spite of 
all this they are little subject to the 
attacks of such enemies as birds, and 
Bates attributed this to the fact that 
the juices of their bodies are unpalat- 
able. According to him their striking 
and conspicuous pattern is of the nature 
of a warning coloration, advertising 
their disagreeable properties to possible 
enemies. A bird which had once at- 
tempted to eat one would find it little 
to its taste. It would thenceforward 
associate the conspicuous pattern with 
a disagreeable flavor and in future leave 
such butterflies severely alone. The 
more conspicuous the pattern the more 
readily would it be noticed by the 
enemy, and so it would be of advantage 
to the Ithomiine to possess as striking a 
pattern as possible. Those butterflies 
showing a tendency to a more con- 
spicuous pattern would be more im- 
of Heredity 
mune to the attacks of birds and so 
would have a better chance of leaving 
progeny than those with a less con- 
spicuous pattern. In this way varia- 
tions in the direction of greater con- 
spicuousness would be accumulated 
gradually by natural selection, and so 
would be built up in the Ithomiine the 
striking warning coloration by which 
it advertises its disagreeable properties. 
Such is the first step in the making of 
a mimicry case—the building up through 
natural selection of a conspicuous pat- 
tern in an unpalatable species by means 
of which it is enabled to advertise its 
disagreeable properties effectively and 
thereby secure immunity from the at- 
tacks of enemies which are able to ap- 
preciate such advertisement. Such pat- 
terns and colors are said to be of a 
‘warning’ nature. The existence of an 
unpalatable model in considerable num- 
bers is the first step in the production 
of a mimetic resemblance through the 
agency of natural selection. 
BEGINNING OF CHANGE 
‘“We come back now to our Pierines 
which must be assumed to show the 
general characters and coloration of the 
family of whites to which they belong. 
Theoretically they are not specially 
protected by nauseous properties from 
enemies and hence their conspicuous 
white coloration renders them especially 
liable to attack. If, however, they could 
exchange their normal dress for one 
resembling that of the Ithomiines it is 
clear that they would have a chance of 
being mistaken for the latter and con- 
sequently of being left alone. More- 
over, in certain cases these Pierines have 
managed to discard their normal dress 
and assume that of the Ithomiines. 
On theoretical grounds this must clearly 
be of advantage to them, and being so 
might conceivably have risen through 
the action of natural selection. This 
indeed is what is supposed to have taken 
place on the theory of mimicry. Those 
Pierines which exhibited a variation of 
color in the direction of the Ithomiine 
‘model’ excited distrust in the minds 
of would-be devourers, who had learned 
from experience to associate that par- 
ticular type of coloration with a dis- 
