400 THE ORIGIN OF SPECIES 



as it remains in its mother's womb or in the egg, or as long as it is 

 nourished and protected by its parent, whether most of its char- 

 acters are acquired a little earlier or later in life. It would not 

 signify, for instance, to a bird which obtained its food by having 

 a much-curved beak, whether or not while young it possessed a 

 beak of this shape, as long as it was fed by its parents. 



I have stated in the first chapter, that at whatever age a varia- 

 tion first appears in the parent, it tends to reappear at a corre- 

 sponding age in the offspring. Certain variations can only appear 

 at corresponding ages ; for instance, peculiarities in the caterpillar, 

 cocoon, or imago states of the silk-moth; or, again, in the full- 

 grown horns of cattle. But variations which, for all that we can 

 see, might have first appeared either earlier or later in life, like- 

 wise tend to reappear at a corresponding age in the offspring and 

 parent. I am far from meaning that this is invariably the case, and 

 I could give several exceptional cases of variations (taking the 

 word in the largest sense) which have supervened at an earlier age 

 in the child than in the parent. 



These two principles, namely, that slight variations generally 

 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 bull-dog, though 

 so different, are really 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 ac- 

 quired 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 domesti- 

 cation — 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, 



