Chap. XHI. EMBRYOLOGY. 445 



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 

 nearly acquired their full amount of proportional differ- 

 ence. 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 care- 

 fully 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, fantails, 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 productions. But 

 when the nestling birds of these several breeds were 

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

 guished from each other, yet their proportional differ- 

 ences in the above specified several points were in- 

 comparably 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 



