xliii, xliv] (sor } 
butterflies, but I do suggest that even if it be proved that 
they are not so now, it by no means follows that they never 
were. 
It may be further objected that if the selective force of 
birds is no longer as strong as it was, what influence main- 
tains those accurate cases of mimicry with which we are all 
familiar? To this one may reply that we are ignorant of the 
relative power of the forces which guide development. So 
long as existence depended upon favourable variation, sexual 
selection may have been too weak to prevent such variation. 
Sexual selection may, however, be sufficient in some species 
to maintain facies which have been perfected through long 
periods of evolution. Such suggestions are merely specu- 
lative, but they may serve to remind those who would lay 
down laws for mimetic development, how complicated both in 
their nature and in their effect, are the influences which guide 
the course of evolution. 
In discussing the Batesian and Miillerian theories, Prof. 
Packard’s paper lays much stress on the explanation that 
resemblance between butterflies is due to convergence brought 
about by similarity in their surroundings. Thus we read— 
‘From the facts regarding these local varieties thus stated 
by Bates, we seem warranted in ascribing the mimetic re- 
semblance to convergence, or exposure to the same conditions 
of light, heat, moisture, etc., affecting all the individuals of a 
variety simultaneously rather than to what is vaguely called 
natural selection.”” And again—“ The colour and markings 
of animals in general are primarily due to the action of light 
and the colour of the environment or background. To sup- 
pose that in the case of butterflies alone the colours of the 
mimics are due to the attacks of birds, whereas remarkably 
few butterflies, as we have seen, are ever eaten by them, is a 
cause so inadequate, so limited in its scope and so one-sided, 
that it is no wonder the hypothesis has so many opponents.” 
In these observations, we seem again to have the idea of 
climatic influence, and it appears to me to be desirable here 
to quote the words of Professor Poulton in his paper read 
before the Linnean Society in March 1898—‘ There is 
something attractive and plausible in the suggestion that the 
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