habit were protectively colored it simply would not have a chance to exist. It lies fearlessly exposed on the bare stones during the brightest hours of the tropical day, a time when almost every other animal is skulking out of sight. Lying upon all the stones round about are the genuine droppings of birds; and when one sees the two together it is difficult to say whether one is most struck with the originality of the idea, or the extraordinary audacity with which the _rôle_ is carried out.* * It is a considerable responsibility to be the sole witness to this comedy--though I saw it repeated a dozen times subsequently--but, fortunately for my veracity, I have since learned from Mr. Kirby of the British Museum that, there is an English beetle, the _Cionus Blattaria_, the larval form of which "operates" in a precisely similar way. It will be apparent from these brief notes that mimicry is not merely an occasional or exceptional phenomenon, but an integral part of the economy of nature. It is not a chance relation between a few objects, but a system so widely authorized that probably the whole animal kingdom is more or less involved in it; a system, moreover, which, in the hands of natural selection, must ever increase in intricacy and beauty. It may also be taken for granted that a scheme so widespread and so successful is based upon some sound utilitarian principle. That principle, I should say, was probably its _economy_. Nature does everything as simply as possible, and with the least expenditure of material. Now consider the enormous saving of muscle and nerve, of instinct and energy, secured by making an animal's lease of life to depend on passivity rather than activity. Instead of having to run away, the creature has simply to keep still; instead of having to fight, it has but to hide. No armor is needed, no powerful muscle, no expanse of wing. A few daubs of color, a little modelling of thorax and abdomen, a deft turn of antennæ and limb, and the thing is done.