Correlation 



radiating from the sand on which these creatures 

 dwell. 



White quills do not wear well either in 

 domestic birds or in wild albinos. This may 

 explain why it is that when a white wild species 

 of bird has any black in its plumage the black is 

 almost invariably on the tips of the wings. 



White quill-feathers are one of the commonest 

 variations observed in domesticated birds, never- 

 theless they are as rare as complete whiteness 

 among birds in their natural state. 



A chestnut or bay colour in mammals appears 

 to be correlated with a high rate of speed, as in 

 the thoroughbred horse. This perhaps explains 

 why so many of the swiftest species of antelope, 

 such as the hartebeests and sassaby (Damaliscus 

 lunatus], are chestnut bay in colour. It is further 

 a remarkable fact that in the Black-buck (Antilope 

 cervicapra] and the Nilgai (Boselaphus trago- 

 camelus] the females, which are faster than the 

 males, are not black or grey like their respective 

 males, but reddish. 



Wild turkeys are bronze ; tame ones are black 

 more often than any other colour. This may be 

 due to the fact that in them nigritude is cor- 

 related with the power to resist damp. Among 

 human beings those races which live in very 

 swampy districts are often intensely black. 



It is a significant fact that those domestic 

 animals which are bred for speed or for fighting 



363 



