248 DEVELOPMENT AND EMBRYOLOGY. [Chap. XIV. 



heavy cart-horses, I find that this is by no means the 

 case. 



As we have conclusive evidence that the breeds of 

 the Pigeon are descended from a single wild species, I 

 compared the young within twelve hours after being 

 hatched; I carefully measured the proportions (but will 

 not here give the details) of the beak, width of mouth, 

 length of nostril and of eyelid, size of feet and length 

 of leg, in the wild parent-species, in pouters, fantails, 

 runts, barbs, dragons, carriers, and tumblers. Now 

 some of these birds, when mature, differ in so extraordi- 

 nary a manner in the length and form of beak, and in 

 other characters, that they would certainly have been 

 ranked as distinct genera if found in a state of nature. 

 But when the nestling birds of these several breeds were 

 placed in a row, though most of them could just be dis- 

 tinguished, the proportional differences in the above 

 specified points were incomparably less than in the full- 

 grown birds. Some characteristic points of difEerenee 

 —for instance, that of the width of mouth — could hardly 

 be detected in the young. But there was one remark- 

 able exception to this rule, for the young of the short- 

 faced tumbler differed from the young of the wild rock- 

 pigeon and of the other breeds, in almost exactly the 

 same proportions as in the adult state. 



These facts are explained by the above two principles. 

 Fanciers select their dogs, horses, pigeons, &c., for breed- 

 ing, when nearly grown up : they are indifferent whether 

 the desired qualities are acquired earlier or later in 

 life, if the full-grown animal possesses them. And 

 the cases just given, more especially that of the pigeons, 

 show that the characteristic differences which have been 

 accumulated by man's selection, and which give value to 



