176 Darwin, and after Darwin. 



of species whose diagnostic characters have been 

 worked out with most completeness, I restricted 

 the inquiry to specific distinctions of colour, not 

 only for the sake of having a uniform basis for 

 comparisons, but still more because it seemed that 

 the argument from our ignorance of possibly un- 

 known uses could be more successfully met in the 

 case of slight differences of colour or of shading, 

 than in that of any differences of structure or of 

 form. Finally, after tabulating all the differences of 

 colour which are given as diagnostic of each species 

 in a genus, and placing in one column those which 

 may conceivably be useful, while placing in another 

 column those of which it appeared inconceivable 

 that any use could be suggested, I added up the 

 figures in the two columns, and thus obtained a 

 grand total of all the specific characters of the 

 genus in respect of colours, separated into the two 

 classes of conceivably useful and apparently useless. 

 Now, in all cases the apparently useless characters 

 largely preponderated over the conceivably useful 

 ones ; and therefore I abundantly satisfied myself 

 regarding the accuracy of my previous statement, 

 that a large proportional number — if not an actual 

 majority — of specific characters belong to the latter 

 category. 



The following is a brief abstract of these results. 



With respect to Birds, a large number of cases 

 were collected wherein the characters of allied 

 species differ from one another in such minute 

 respects of colour or shading, that it seemed unrea- 

 sonable to suppose them due to any selective 

 value to the birds in question. It is needless — 



