224 DOMESTIC PIGEONS. Chap. Vr. 



vary at the same time. When several breeds have once been 

 formed, their intercrossing aids the progress of modification, 

 and has even produced new sub-breeds. But as, in the con- 

 struction of a building, mere stones or bricks are of little 

 avail without the builder's art, so, in the production of new 

 races, selection has been the presiding power. Fanciers can 

 act by selection on excessively slight individual differences, as 

 well as on those greater differences which are called sports. 

 Selection is followed methodically when the fancier tries to 

 improve and modify a breed according to a prefixed standard 

 of excellence ; or he acts unmethodically and unconsciously, 

 by merely trying to rear as good birds as he can, without any 

 wish or intention to alter the breed. The progress of selection 

 almost inevitably leads to the neglect and ultimate extinction of 

 the earlier and less improved forms, as well as of many inter- 

 mediate links in each long line of descent. Thus it has come to 

 pass that most of our present races are so marvellously distinct 

 from each other, and from the aboriginal rock-pigeon. 



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