It was found in the limestone hills at Busan, the situation of all others where mosses are most plentiful and delicate, and where they partially clothe most of the protruding masses of rock." _How these Imitations have been Produced._ To many persons it will seem impossible that such beautiful and detailed resemblances as those now described--and these are only samples of thousands that occur in all parts of the world--can have been brought about by the preservation of accidental useful variations.

But this will not seem so surprising if we keep in mind the facts set forth in our earlier chapters--the rapid multiplication, the severe struggle for existence, and the constant variability of these and all other organisms.

And, further, we must remember that these delicate adjustments are the result of a process which has been going on for millions of years, and that we now see the small percentage of successes among the myriads of failures.

From the very first appearance of insects and their various kinds of enemies the need of protection arose, and was usually most easily met by modifications of colour.

Hence, we may be sure that the earliest leaf-eating insects acquired a green colour as one of the necessities of their existence; and, as the species became modified and specialised, those feeding on particular species of plants would rapidly acquire the peculiar tints and markings best adapted to conceal them upon those plants.