3io SCIENCE FROM AN EASY CHAIR 



could no longer see the dark-green area at all one only 

 saw a white spot on a continuous dark ground, the dark- 

 green and the black were merged into one. That is no 

 doubt due to the powerful stimulation of the sensitive 

 " retina " of the eye by the white light of the spot ; the 

 feeble stimulation by the dark-green and black, though 

 these remain physically as distinct from one another as 

 before, ceases to affect the brain, which is, as it were, 

 entirely occupied with the strong white spot. This, 

 according to Mr. Thayer, is the value to butterflies and 

 other animals of a violently contrasted white spot or 

 band on a dark general colouring. The fringe of white 

 dots and connected white flakes nearer the centre of the 

 wing common on the wings of butterflies has, similarly, 

 the result of rendering the wing-outline imperceptible and 

 the butterfly invisible. Many such relations of colour 

 spots and bands, as well as of dark and light markings, 

 have been elucidated by Mr. Thayer, and will be illustrated 

 by coloured drawings in the book which he is preparing 

 on the subject. 



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 experi- 



