VIII ORIGIX AXD USES OF COLOUR IX AXDIALS 217 



by some change in the colour of the eggs, or in the structure 

 or position of the nest, or by the increased care which the 

 parents bestow upon the eggs. In this way the various 

 divergences which now so often puzzle us may have arisen. 



Colour as a Means of liecognition. 



If we consider the habits and life-histories of those animals 

 which are more or less gregarious, comprising a large pro- 

 portion of the herbivora, some carnivora, and a considerable 

 number of all orders of bii'ds, Ave shall see that a means of 

 ready recognition of its own kind, at a distance or during 

 rapid motion, in the dusk of t^Wlight or in partial cover, 

 must be of the greatest advantage and often lead to the pre- 

 servation of life. Animals of this kind wiU not usually 

 receive a stranger into their midst. While they keep together 

 they are generally safe from attack, but a solitary straggler 

 becomes an easy prey to the enemy ; it is, therefore, of the 

 highest importance that, in such a case, the wanderer should 

 have every facility for discovering its companions wdth cer- 

 tainty at any distance within the range of vision. 



Some means of easy recognition must be of vital im- 

 portance to the young and inexperienced of each flock, and it 

 also enables the sexes to recognise their kind and thus avoid 

 the evils of infertile crosses ; and I am inclined to believe that 

 its necessity has had a more widesj^read influence in deter- 

 mining the diversities of animal coloration than any other 

 cause whatever. To it may probably be imputed the singular 

 fact that, whereas bilateral symmetry of coloration is very 

 frequently lost among domesticated animals, it almost uni- 

 versally prevails in a state of nature ; for if the two sides of 

 an animal were unlike, and the diversity of coloration among 

 domestic animals occurred in a wild state, easy recognition 

 would be impossible among numerous closely allied forms. ^ 



^ Professor Wm. H. Brewer of Yale College has shown that the white 

 murks or the spots of domesticated animals are rarely sATumetrical, but have 

 a tendency to appear more frequently on the left side. This is the case with 

 horses, cattle, dogs, and swine. Among wild animals the skunk varies con- 

 siderably in the amount of white on the body, and this too was found to be 

 usually greatest on the left side. A close examination of numerous striped or 

 spotted species, as tigers, leopards, jaguars, zebras, etc., showed that the 

 bUateral symmetry was not exact, although the general effect of the two sides 



