Although the extraordinary phenomena of mimicry are now pretty generally known to science, few workers have yet had the opportunity of studying them in nature. But no study in natural history depends more upon observation in the field; for while in the case of a few mimetic forms--the _Heliconidæ_, for example--the imitated form is also an insect, and the two specimens may be laid side by side in the cabinet at home, the great majority of mimetic insects are imitations of objects in the environment which cannot be brought into comparison with them in the drawers of a museum. Besides this, it is not only the form but the behavior of the mimetic insect, its whole habit and habitat, that have to be considered; so that mere museum contributions to mimicry are almost useless without the amplest supplement from the field naturalist. I make no further apology, therefore, for transcribing here a few notes bearing upon this subject from journals written during a recent survey of a region in the heart of Africa--the Nyassa-Tanganyika plateau--which has not yet been described or visited by any naturalist. The preliminaries of the subject can be mastered in a moment even by the uninitiated, and I may therefore begin with a short preface on animal coloring in general. Mimicry depends on resemblances between an animal and some other object in its environment of which it is a practical gain to the creature to be a more or less accurate copy. The resemblance may be to any object, animate or inanimate. It may be restricted to color, or it may extend to form, and even to habit; but of these the first is by far the most important.