THE LAWS OF VAEIABILITY. 71 



tion, and hatched their eggs at the same time with the 

 common ducks of the same place. 



Many cases of non-inheritance apparently result from 

 the conditions of life continually inducing fresh yaria- 

 bility. We have seen that when the seeds of pears, plums, 

 apples, etc., are sown, the seedlings generally inherit some 

 degree of family likeness. Mingled with these seedlings, 

 a few, and sometimes many, worthless, wild-looking plants 

 commonly appear, and their appearance may be attributed 

 to the principle of reversion. But scarcely a single seed- 

 ling will be found perfectly to resemble the parent-form ; 

 and this may be accounted for by constantly recurring 

 Tariability induced by the conditions of life. 



STEPS BT WHICH DOMESTIC EACES HATE BEEN PRODUCED. 



Oriein of Some efEect may be attributed to the direct 



Species, and definite action of the external conditions 

 page • Qf 2if e, and some to habit ; but he would be a 

 bold man who would account by such agencies for the 

 differences between a dray and race horse, a greyhound 

 and blood-hound, a carrier and tumbler pigeon. One of 

 the most remarkable features in our domesticated races is 

 that we see in them adaptation, not, indeed, to the ani- 

 mal's or plant's own good, but to man's use or fancy. 

 Some Tariations useful to him have probably arisen sud- 

 denly, or by one step ; many botanists, for instance, be- 

 lieve that the fuUer's teasel, with its hooks, which can not 

 be rivaled by any mechanical contrivance, is only a variety 

 of the wild Dipsacus ; and this amount of change may 

 have suddenly arisen in a seedling. So it has probably 

 been with the turnspit-dog ; and this is known to have 

 been the case with the ancon sheep. But when we compare 

 the dray-horse and race-horse, the dromedary and camel. 



