GENERAL PRINCIPLES OF BREEDING. 39 



of nature, and of the various causes that serve 

 to disturb this uniformity in our domesticated 

 animals when subjected to changed conditions 

 of climate or nutrition. I have also treated of 

 the effect of heredity, which makes of the off- 

 spring the sum or aggregation of the qualities 

 that existed in its progenitors, and of the oppos- 

 ing law of evolution or spontaneity which tends 

 to give to each animal a character of its own. 

 I now propose to consider how these known 

 laws and forces may be utilized in the forma- 

 tion of breeds; and, at the threshold of this 

 division of my subject, it is necessary that we 

 should understand what is meant by the terms 

 used. 



The animal kingdom is divided by natural- 

 ists into four great loranches Radiata y Mollusca, 

 Articulala, and Vertebrate. These branches are 

 again divided into classes. The Vertebrata, to 

 which branch all our domesticated animals be- 

 long, are divided into eight classes, the last of 

 which are the Mammalia, embracing all ani- 

 mals that give suck to their young. These 

 classes are divided into genera, and these again 

 into species. For example: we have the genus 

 Equus, of which the horse, the ass, the zebra 

 and the quagga are species; and these differ- 

 ent species are again divided, with reference 

 to certain peculiarities, into breeds. A breed, 

 therefore, is a classification by which we dis- 



