CHAPTER I ON VARIATION. 



PRELIMINARY. 



LL species are not equally variable. Some species 

 vary little or not at all, even under domestication. 

 Thus the varieties of the turkey (Meleagris gallopavo} 

 and the guinea-fowl (Numida meleagris} are few, and 

 are confined to albinistic or melanistic conditions. 

 The barnyard fowl (Galhts j/.), on the other hand, 

 varies enormously, as does also the pigeon (Columba 

 livia}. Among domesticated Mammalia the variations 

 of cats (Felis domestica] are few as compared with those 

 of dogs (Cams j/.). 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 {Eutcenia sir tails} varies exceedingly, while 

 the variations of the allied ribband snake (Eutania 

 saurita) are minute or none. But little variation has 

 been observed in the polar bear (Ursus marittmus), 

 while the common bear (17. arctos} presents many vari- 

 eties. Similar conditions are found among fishes. Thus 

 the larger species of pike, the muskallonge (Lucius nobi- 

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

 latus} are constant in their characters, while the small 

 pickerel (Z. vermiculatus} presents numerous varieties. 



