GENERAL PRINCIPLES OF BREEDING. 19 



the whole back and wings; the double black wing bars were 

 equally conspicuous; the tail was exactly alike in all its 

 characters, and the croup was pure white; the head, how- 

 ever, was tinted with a shade of red, evidently derived from 

 the spot, and was of a paler blue than in the rock pigeon, as 

 was the stomach. So that two black barbs, a red spot and 

 a white fan tail, as the four purely-bred grandparents, pro- 

 duced a bird of the same general blue color, together with 

 every characteristic mark, as in the wild Columba livid, or 

 rock pigeon.* 



This tendency to reversion in different breeds 

 of domestic animals when crossed accounts for 

 many of the disappointments which breeders 

 experience in their efforts to improve their 

 stock, and serves greatly to complicate the 

 breeding problem. 



MODIFICATIONS PRODUCED BY CHANGED CONDI- 

 TIONS OF LIFE. 



It is quite certain, from what we know of 

 the effect of climate and of changed habits 

 upon animals in a state of domestication, that 

 if two branches of the same tribe or species, 

 essentially alike in every feature, should, by 

 some chance, become separated and compelled 

 to subsist under widely different conditions of 

 life, being left entirely to themselves and the 

 operation of natural laws, in course of time a 



* Those who have a desire to investigate this subject, as illus- 

 trated by the breeding of pigeons, will find a very full history of 

 the various breeds, their processes of formation, and the effects of 

 selection and crossing of breeds, in Darwin's " Variations of Ani- 

 mals and Plants under Domesti cation," Vol. I, pp. 163 to 272. 



