will practically coincide. But the application of any such principle 
to the phenomena of Insect mimicry is attended with serious 
difficulty. The cases to be explained are not scanty in number, but 
abundant. Then again, many of the resemblances occur, as we have 
seen, between Insects widely separated in point of affinity. Take 
the Lycoid assemblage that we have previously mentioned. Is it 
probable that Beetles, Braconids, Wasps, Bugs, Moths and two- 
winged Flies should all have been impelled by internal causes to 
reach the same stage of colour-development at the same epoch of 
their phylogenetic history? And if this be considered not imposs- 
ible, why should the various members of this assemblage be all 
found together in the same place, many of them actually on the 
same tree? We have already given attention to the fact that the 
forms resembling each other are as a general rule inhabitants of 
the same localities. It is not by any means clear how this is to be 
explained on the theory of internal causes of similar development. 
It is true that, as we have seen, there are sporadic cases of resem- 
blances that have to all appearance developed independently of 
one another. But why should they be so few in comparison with 
the enormous number of instances, which occur under the condi- 
tions of a common habitat? There is no apparent reason, under the 
theory of internal causes, why there should be any connection 
between the likeness and the locality. 
Those of my audience who happen to be acquainted with my 
writings on this subject, will have anticipated the solution of the 
problem which I should myself favour. I should find myself in 
agreement with Mr. THAYER to the extent of believing, with him, 
that these resemblances are of service to the forms exhibiting 
them, and that their establishment and survival have taken place 
under the control of natural selection. But I cannot follow him 
in the opinion that all the patterns which we have been conside- 
ring, and which are so widely adopted by Insects of such different 
affinities, are calculated to render their possessors invisible against 
their background. On the contrary, and I think the experience of 
most observers will here bear me out, it appears to me that the 
Butterflies, which exhibit these brilliant and variegated colours, are 
for the most part conspicuous on the wing. Moreover, many of 
them adopt a slow, deliberate mode of flight, which seems to court 
observation. This is certainly the case with members of the genera 
Mylothris and Amauris, and with several of the Acr&as. We have 
now a good deal of evidence that some of these forms are unpalat- 
able to certain Birds, and are at any rate not taken by preference. 
