not be perfect if it did not include a delicate gradation of actual color, from 

 brownest above to bluest below, to cancel the effect of the bluish sky-light 

 and shine on their upper surfaces, and the brownish shadow, with brown earth- 

 reflections, on their lower. Cold white is usually required for the bright 

 climax of the shade gradation, and cold white amply meets the color require- 

 ment also. It is likely that few but artists will feel the validness of our state- 

 ment of this subtler element of the principle, although anyone can learn to 

 see the existent gradation of ' color' on most counter-shaded animals. 



The reader has now been given a fairly exhaustive description of the main 

 elements of the new principle, which through its various windings and with its 

 various remarkable concomitants we are about to follow into several branches 

 of the animal kingdom. Among the lower orders, it is more or less largely 

 supplanted by another great principle, namely, that of Mimicry, which we 

 will define and differentiate in Chapter II. 



Before closing this introductory chapter, however, we must give an account 

 of the earlier, independent partial discovery of the principle of counter shading 

 in the animal kingdom, by Prof. Edward B. Poulton, of Oxford University. 

 Professor Poulton has been one of my father's most enthusiastic listeners, 

 and is one of the few naturalists who have given proof of completely under- 

 standing the subject. In his introduction to my father's article in Nature 

 he generously seeks to minimize the importance of his own partial predis- 

 covery of the principle. 



The case is thus stated by my father in the above-mentioned article: 



"Since publishing my papers in 'The Auk' for April and October, 1896, 

 I find that Prof. Poulton perceived years before their appearance the power 

 of a counter-grading of light to make the round surface of a pupa appear 

 flat, and in another case the power of light color in a depression to make the 

 concavity disappear. In both of these cases he perceived the very Law of 

 Light-and-Shade on which the fact of Protective Coloration rests, and recognized 

 the fact itself in these instances. In his 'Notes in 1886 upon Lepidopterous 

 Larvas, etc.,' read April 6, 1887, he says (Trans. Ent. Soc. Lond., 1887, p. 



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