82 Journal of Travel and Natural History 



will, I think, be admitted that the relation bet^veen the two series 

 of facts in the colouring and nidification of birds has been suffi- 

 ciently established. There are, it is true, a few apparent and some 

 real exceptions, which I shall consider presently ; but they are too 

 few and unimportant to weigh much against the mass of evidence 

 on the other side, and may for the present be neglected. Let us 

 then, consider what we are to do with this unexpected set of 

 correspondences between gi-oups of phenomena which, at first 

 sight, appear so disconnected. Do they fall in with any other 

 groups of natural plienomena? Do they teach us anything of the 

 way in which nature works, and give us any insight into the 

 causes Avliich have brought about the marvellous variety, and 

 beauty, and harmony of living things ? I believe we can answer 

 these questions in the affirmative ; and I may mention, as a suffi- 

 cient proof, that these are not isolated facts, that I was first led to 

 see their relation to each other by the study of an analogous 

 though distinct set of phenomena among insects, that of protective 

 resemblance and " mimicry." 



On considering this remarkable series of facts, the first thing we 

 are taught by them seems to be, that there is no incapacity in the 

 female sex among birds, to receive the same bright hues and 

 strongly contrasted tints with which their partners are so often 

 decorated, since whenever they are protected and concealed dur- 

 ing the period of incubation tlicy are similarly adorned. The fair 

 inference is, that it is chiefly due to the absence of protection or 

 concealment during this important epoch, that gay and conspicu- 

 ous tints are withheld or left undeveloped. The mode in which 

 this has been effected is very intelligible, if we admit the action of 

 natural and sexual selection. It would appear from the numerous 

 cases in which both sexes are adorned with equally brilliant colours 

 (Avhile both sexes are rarely armed] Avith equally developed offen- 

 sive and defensive weapons when not required for individual 

 safety), that the normal action of " sexual selection" is to develop 

 colour and beauty in both sexes, by the preservation and multipli- 

 cation of all varieties of colour in either sex which are pleasing to 

 the other. The female bird, however, while sitting on her eggs in 

 an uncovered nest, is especially open to the attacks of enemies, 

 and any modification of colour which rendered her more conspicu- 

 ous would lead to her destruction and that of her offspring. All 

 •variations of colour in this direction in the female, would therefore 

 sooner or later be exterminated, while such modifications as 



