tures were purely and simply " colored like their surroundings" they would not 

 be inconspicuous at all. This has already been explained by articles in several 

 scientific and popular magazines, but the explanation must be repeated here 

 in full for the benefit of those who have not seen the former expositions of the 

 discovery. What people commonly fail to perceive in connection with this 

 matter, is that the exposition is really that of a discovery, i. e., of an indis- 

 putable optical fact, hitherto unnoticed, and not merely that of one more 

 theory. It is the revelation of how animals' wonderful inconspicuousness in 

 their normal haunts, recognized for centuries but in its essence never under- 

 stood, is really achieved. That is, not a description of any course of evolution 

 or process of pigmentation, but the revelation of the manner in which the 

 existent system of coloration renders animals nearly invisible on their native 

 heath. 



I will quote, with slight modifications, from the original article published 

 in 1896, and from that published in Nature in 1902. 



"The newly-discovered law in its application to animals may be stated 

 thus: Animals are painted by Nature darkest on those parts which tend to be 

 most lighted by the sky's light, and vice versa. The accompanying diagram 

 illustrates this statement. 



ABC 



" Animals are colored by Nature as in A, the sky lights them as in B, and 

 the two effects cancel each other, as in C. The result is that their grada- 

 tion of light-and-shade, by which opaque solid objects manifest themselves to 

 the eye, is effaced at every point, the cancellation being as complete at one 



14 



