X PEEFACE. 



tinguish certain male birds and insects, which is directly- 

 opposed to the view held by Mr. Darwin and so well 

 explained and illustrated in his great work on "The 

 Descent of Man and on Selection in Kelation to Sex." 

 Being strongly impressed with the importance and 

 fundamental truth of this theory, I published my first 

 sketch of the subject in Macmillans Magazine in order 

 that it might have the benefit of criticism before making 

 it public in a more permanent form. Taking advantage 

 of some suggestions from Mr. Darwin and from a 

 few other correspondents^ I have made considerable 

 additions to the original essay and have rearranged, 

 and I trust strengthened the argument, which I now 

 hope may attract the attention of all who are interested 

 in the subject. I may be allowed here to remark, that 

 my theory cannot be properly understood without 

 reading the whole chapter on The Colours of 

 Animals ; because the view set forth and illustrated 

 in the first part of that chapter — that colour in nature 

 is normal, and that its presence hardly requires to 

 be accounted for so much as its absence — is an essential 

 part of the theory. 



Croydon, April, 1878. 



