Correlation 



may be due to a correlation with the power of 

 withstanding intense dry heat rather than to its 

 rendering them inconspicuous to their foes. 



As other examples of correlation we may cite 

 the correlation which seems to obtain between 

 short canine teeth and the absence of a hairy 

 covering to the body. This phenomenon is 

 observed both in men and pigs. Hairless dogs 

 almost invariably have their teeth but poorly 

 developed. 



Darwin called attention to the connection 

 between a short beak and small feet in pigeons ; 

 we see the same phenomenon in the dwarf breed 

 of ducks known as call-ducks. 



A curious correlation exists between fowls' 

 eggs with brown shells and the incubating habit. 

 Fanciers have long tried in vain to produce a 

 hen that lays brown eggs without becoming 

 " broody" at certain seasons. 



Among fowls, long legs are invariably cor- 

 related with a short tail, as is well seen in the 

 Malay breed. This correlation may explain the 

 short tails of wading birds. Short-legged fowls, 

 like Japanese bantams, have long tails, and it is 

 significant that the short-legged Weka Rails 

 (Ocydromus) of New Zealand have unusually 

 long tails for the family. In this connection we 

 may say that the tail-like plumes of the cranes 

 are not tail-feathers, but the tertiary feathers of 

 the wings. As egrets also have long trains of 



365 



