Protective Resemblances. 143
of yellow, ash, brown, and red is found here, and in many specimens there occur patches and spots formed of small black dots, so closely resembling the way in which minute fungi grow on leaves that it is almost impossible at first not to believe that fungi have grown on the butterflies themselves!
If such an extraordinary adaptation as this stood alone, it would be very difficult to offer any explanation of it; but although it is perhaps the most perfect case of protective imitation known, there are hundreds of similar resemblances in nature, and from these it is possible to deduce a general theory of the manner in which they have been slowly brought about. The principle of variation and that of a natural selection,a or survival of the fittest, as elaborated by Mr. Darwin in his celebrated 66 Origin of Species,a offers the foundation for such a theory; and I have myself endeavored to apply it to all the chief cases of imitation in an article published in the West-minster Review for 1867, entitled, a Mimicry, and other Protective Resemblances among Animals,a to which any reader is referred who wishes to know more about this subject.
In Sumatra monkeys are very abundant, and at Lobo Raman they used to frequent the trees which overhang the guard-house, and give me a fine opportunity of observing their gambols. Two species of ^Semnopitheeus were most plentiful a monkeys of a slender form, with very long tails. Not being much shot at, they are rather bold, and remain quite unconcerned when natives alone are present; but when I came out to look at them, they would stare for a minute or two and then make off. They take tremendous leaps from the branches of one tree to those of another a little lower, and it is very amusing when one strong leader takes a bold jump, to see the others following with more or less trepidation; and it often happens that one or two of the last seem quite unable to make up their minds to leap till the rest are disappearing, when, as if in desperation at being left alone, they throw themselves frantically into the air, and often go crashing through the slender branches and fall to the ground.
A very curious ape, the siamang, was also rather abundant, but it is much less bold than the monkeys, keeping to the virgin forests and avoiding villages. This species is allied to the little long-armed apes of the genus Hylobates, but is consider-