CHAPTER I— ON VARIATION. 



J. 



PRELIMINARY. 



\ LL species are not equally variable. Some species 

 :^J^ vary little or not at all, even under domestication. 

 Thus the varieties of the turkey {Aleleagris gallopavd) 

 and the guinea-fowl (^Niimida meleagris) are few, and 

 are confined to albinistic or melanistic conditions. 

 The barnyard fowl (^Galliis sp.'), on the other hand, 

 varies enormously, as does also the pigeon {Columba 

 livia). Among domesticated Mammalia the variations 

 of cats {Fclis domestica) are few as compared with those 

 of dogs {Canis sp.). Variability is not peculiar to do- 

 mesticated animals. A large proportion of animals 

 and plants are, in a state of nature, variable, and some 

 of these are much more so than others. The common 

 garter-snake (^Euicenia sir talis) varies exceedingly, while 

 the variations of the allied ribband snake {Eidcenia 

 saurita) are minute or none. But little variation has 

 been observed in the polar bear {Ursus maritimus), 

 while the common bear (^U. arctos) presents many vari- 

 eties. Similar conditions are found among fishes. Thus 

 the larger species of pike, the muskallonge [^Lucius nobi- 

 lior), the pike (Z. estor), and the pickerel (Z. vermicu- 

 latus) are constant in their characters, while the small 

 pickerel (Z. vermiculatus) presents numerous varieties. 



