368 DEVELOPMENT AND EMBRYOLOGY. [CHAP. XIV. 



appear at a not very early period of life, and are inherited at 

 a corresponding not early period, explain, as I believe, all the 

 above specified leading facts in embryology. But first let us look 

 to a few analogous cases in our domestic varieties. Some 

 authors who have written on Dogs, maintain that the greyhound 

 and bulldog, though so different, are re'ally closely allied varieties, 

 descended from the same wild stock ; hence I was curious to see 

 how far their puppies differed from each other: I was told by 

 breeders that they differed just as much as their parents, and 

 this, judging by the eye, seemed almost to be the case ; but on 

 actually measuring the old dogs and their six-days-old puppies, 

 I found that the puppies had not acquired nearly their full 

 amount of proportional difference. So, again, I was told that the 

 foals of cart and race-horses breeds which have been almost 

 wholly formed by selection under domestication differed as much 

 as the full-grown animals ; but having had careful measurements 

 made of the dams and of three-days-old colts of race and 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 extraordinary 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 

 distinguished, the proportional differences in the above specified 

 points were incomparably less than in the full-grown birds. 

 Some characteristic points of difference for instance, that of the 

 width of mouth could hardly be detected in the young. But 

 there was one remarkable 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 bvc'ie above two principles. Fanciers 

 select their dogs, horses, pif sons, &c., for breeding, 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 his 

 breeds, do not generally appear at a very early period of life, and 



