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affinity. Some of the most striking are those between Insects of 
different orders. 
3. They are peculiarly liable to occur in Insects of-the female sex. 
4. They are, speaking generally, found only between the 
inhabitants of the same region. 
5. They may affect one phase of a seasonally dimorphic Insect 
differently from the other. 
6. No structure or detail of organisation is involved in these 
resemblances except in so far as a modification therein may assist 
in producing a superficial likeness in aspect or behaviour. 
7. In the production of these resemblances the same effect is 
often brought about by different means. 
8. Every transition exists between a likeness, which is so remote 
as to be fairly disputable, and a resemblance, which may even 
deceive a skilled observer. 
9. In some cases there may be great disparity in point of 
numbers between the forms linked together by community of 
aspect. In other cases the numbers may be nearly equal. 
10. The combinations of two or more forms resembling one 
another are in many cases not isolated, but are often connected with 
other combinations by a more or less complete series of gradations. 
So far we have been concerned with facts. What is to be said 
about their explanation? We have already seen that these cases of 
resemblance are too numerous to be reasonably considered acci- 
dental; moreover their evident relation with conditions of sex, 
locality and visibility seems of itself to forbid such an interpretation. 
When we consider the fact of the limitation of a given system of 
pattern and coloration to a particular area of the earth's surface, 
and especially when we examine the changes that affect a mimetic 
assemblage in common as we pass from one portion to another of 
such an area, as in the series just now exhibited of successive 
modifications undergone by the same general type of coloration in 
the passage from Guatemala to Peru, we are tempted to conjecture 
that geographical conditions may have some bearing on the matter. 
We may remember that many arctic Animals are white, and that 
both Birds and Mammals inhabiting desert regions are frequently 
assimilated in colour to their sandy surroundings. But if we attempt 
to find in these circumstances an analogy with the phenomena 
under present discussion, we are at once confronted with difficulties 
that may well appear insuperable. The prevailing coloration of 
Animals that live amid snow and sand respectively is with high 
