400 ON THE ORIGIN OF SPECIES 



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 nearly acquired their full amount 

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

 the foals of cart and race-horses differed as much as 

 the full-grown animals ; and this surprised me greatly, 

 as I think it probable that the difference between these 

 two breeds has been wholly caused by selection under 

 domestication ; but having had careful measurements 

 made of the dam and of a three-days old colt of a race 

 and heavy cart-horse, I find that the colts have by no 

 means acquired their full amount of proportional 

 difference. 



As the evidence appears to me conclusive, that the 

 several domestic breeds of Pigeon have descended from 

 one wild species, I compared young pigeons of various 

 breeds, within twelve hours after being hatched ; I 

 carefully measured the proportions (but will not here 

 give details) of the beak, width of mouth, length of 

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

 the wild stock, in pouters, fan tails, runts, barbs, 

 dragons, carriers, and tumblers. Now some of these 

 birds, when mature, differ so extraordinarily in length 

 and form of beak, that they would, I cannot doubt, be 

 ranked in distinct genera, had they been natural pro- 

 ductions. But when the nestling birds of these several 

 breeds were placed in a row, though most of them could 

 be distinguished from each other, yet their proportional 

 differences in the above specified several 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 all its proportions, almost exactly as much 

 as in the adult state. 



The two principles above given seem to me to explain 

 these facts in regard to the later embryonic stages of 



