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34 being seriously studied. When we remember the deadly effects of such "waste products" on the higher vertebrates, and that the yellow pigment found in the wings of many of the Pieridæ are due to "modifications of the ordinary waste products of the organism," we are forced with the authoress to suppose "that the wings of butterflies, being relatively non-vital parts, can have poisonous substances stored up in them without injury to the organism, and that therefore the utilisation of waste products as colouring agents can only occur in cases where the coloured structures are not intimately connected with the blood system."

The standpoint of this book is the physiological demonstration of animal colouration, the nature and elements of the colour itself, and not its evolutionary life-purposes. This treatment is neither sympathetic with, nor destructive to, the general conception of Protective resemblance and Mimicry. Colour alone must of course fall under the domain of Physiology and Chemistry, as, and in the same sense, all animal structure does, but this treatment does not explain its development in variety and markings; it only gives us its composites, and does not demonstrate its action as a force in the struggle for existence. In the last chapter, which is devoted to a discussion of "The relation of facts to theories," a rapid survey is given of the principal and perhaps most popular lines of modern speculation, and if Miss Newbigin has not come to bless, at all events most naturalists will agree with her concluding sentences: ".... in spite of the fluency with which so many people talk of the meaning of colour in organisms, the subject is as incomplete on the theoretical as on the physiological side. It seems reasonable to believe that the two deficiencies are related, and that a little more physiology will arm the theorists with better weapons. In the meantime, we cannot end a book on colour more fitly than by an appeal for more facts."

This volume contains many facts relating to animal colouration, and can be studied as well by a naturalist with a theory as by one who possesses it not. The bibliographical references at the end of the volume will assist a student of this fascinating subject.