While it is the fact that Mr. Thayer has thrown new light on the colour-protection and invisibility of animals, it must be remembered that there are other explanations of certain cases of brilliant colouring in animals besides that which he has so well illustrated. “Warning” colours, recognition marks, and sexually attractive colouring all certainly and demonstrably exist in well-known and well-studied kinds of animals. It is very possible that some of these colour-markings have been produced by a slight change in what were previously “concealing” patterns or colour-markings. The tendency of the human observer is to regard any colour, spot, or pattern on a bird, fish, beast, or insect as a “mark” or distinguishing “sign.” We examine these things at close quarters, and do not, unless we reflect a good deal on the matter and experiment with the object, realise that what is a mark of distinction or recognition when seen at a few inches’ distance may be an illusive and obscuring colour-scheme when seen at a distance of some feet, and in natural and habitual surroundings. It is not unlikely that we shall arrive at definite knowledge of the psychological “sight interpretations” of animals by a further study of this subject. It is in the highest degree probable that the retinal picture produced in an animal’s eye by certain spots of colour, shade, and light exhibited by another animal, are not interpreted by the receptive animal in the same way as they would be by a scrutinising, inquiring, reasoning man, even one who is what we call a “savage.” Moreover, though many English naturalists have travelled and seen “life and light” in the sunny regions of the earth, there are few students of the colour-markings of animals in our museums, especially in great cities, who have adequate experience of what colour-markings really can effect in the way of concealment and illusion when light and surrounding objects are as they are, in the tropics or sub-tropical regions. It is a fashion nowadays in the best-provided museums of natural history to exhibit stuffed beasts, birds, and insects in what are called “their natural surroundings.” The fatal objection to such exhibitions is that were the beasts, birds, and insects placed in their most usual “natural surroundings,” they would be invisible!