CHAPTER III 

 SPECIES AND THEIR DIVISIONS IN DOMESTIC BIRDS 



The three general classes of domestic birds include few spe- 

 cies but many varieties, and, outside of the distinct varieties, 

 an indefinite number of individual types. Where varieties are 

 as numerous as in the fowl, which has about three hundred, and 

 the pigeon, which has a much greater number, the differences 

 between them are often very slight. Sometimes the form of a 

 single small character is the only distinguishing feature. But, 

 if this is a fixed character, the variety is distinct. Where there 

 are so many varieties it is hard to make short, appropriate de- 

 scriptive names for all, if considered simply as varieties. For 

 such diversity there must be a more extended classification. 

 Such a classification, growing gradually with the increase in the 

 number of varieties, will not be consistent throughout. Hence 

 to understand clearly the relations of the artificial divisions 

 of species in domestication we must know what a species is 

 and how these divisions arise. 



Definition of species. Species are the natural divisions of 

 living things. Each plant and animal species retains its dis- 

 tinctive character through long ages because the individuals 

 composing it can produce perfect offspring only (if asexual) of 

 themselves, or (if bisexual) with others of their species. 



The self-isolation of species is well illustrated when similar 

 plants grow together, as grasses in the same field and practi- 

 cally on the same spot ; yet year after year all the old kinds are 

 found and no new ones such as might come from a mixture of 

 two kinds, if they would mix. In the higher animals, where the 

 parent forms are of different sexes, they choose mates of their 



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