4 Dritte allgemeine Sitzung. 
regards the second, we should expect such species to reach nearly 
the same evolutionary stage together, rather than that some should 
reach one stage and others another entirely different one, but the 
same as that reached by certain species of remote affinity. With 
Natural Selection for our explanation such differences are at once 
intelligible. The variation which formed the foundation for selection to 
build upon may Ww ell have been present in certain species of a genus 
but not in others; or slight differences in life-history or the methods 
of adaptation, or the attacks of enemies may have rendered mi- 
micry advantageous for this species but not for that. 
When we pass from mimicry among butterflies to mimicry 
between butterflies and moths the difficulties encountered by all 
theories except Natural Selection become greater because of the 
wider structural difference between model and mimic. To take an 
example, certain species of day-flving Chalcosid moths of Borneo 
mimic Danaine butterflies while others mimic Pierinae. Why should 
part of the Heteroceran group be acted on by external conditions 
to as to cause a superficial resemblance to Danainae the others 
so as to cause a resemblance to Pierinae? Why out of the same 
closely related set of species should some reach the evolutional 
stage of Danainae, the others of Pierinae? Why should the 
models happen to differ from butterflies in general in their slow 
flight and conspicuous appearance, in the similarity of the patterns 
on the under side of the wings to those on the upper side, in the 
fact that they are distasteful to the generality of insect- eating 
animals? Why should the mimics hi appen to belong to a day- 
flying group although moths are as a rule noc turnal? All these 
questions receive an obvious answer when the theory of Natural 
Selection is adopted as the gr aetna of mimicry: they cannot 
be answered by any other existing theory. Under any other 
theory the facts are gr Gist devoid of meaning. . 
When the model belongs to one insect order and the mimic 
to another, difficulties of interpretation, except on the theory of 
Natural Selection, become even greater. Why should the models in 
the vast majority of cases happen to belong to the Hymenoptera 
and to possess stings or other special modes of detence? Why under 
the totally different conditions of Borneo and South Africa should 
a local Xylocopid bee be mimiced by a local Asilid fly (Hyper- 
echia)? Many moths come to resemble transparent-wing ed Hymen- 
optera by the actual loss of scales which were present on their 
wings when they emerged from the pupa. Is anyone bold enough 
to maintain that a resemblance thus caused is due to External 
Internal Causes or to Sexual Selection? 
The assumption that local influences act uniformly on different 
species is by no means justified except in the case of species with 
similar habits and life-histories: Mr. Guy A. K. Marshall has sent 
me a wonderful group of reddish brown or ochreous insects with the 
