13 VARIATION UNDER BOMBSTIGATION. 



on both; but when among individuals, apparently exposed 

 to the same conditions, any very rare deviation, due to 

 some extraordinary combination of circumstances, appears 

 in the parent — say, once among several million individu- 

 als—and it reappears in the child, the mere doctrine of 

 chances almost compels us to attribute its reappearance to 

 inheritance. Every one must have heard of cases of al- 

 binism, prickly skin, hairy bodies, etc., appearing in 

 several members of the same family. If strange and rare de- 

 viations of structure are really inherited, less strange and 

 commoner deviations may be freely admitted to be inherit- 

 able. Perhaps the correct way of viewing the whole 

 subject would be, to look at the inheritance of every 

 character whatever as the rule, and non-inheritance as the 

 anomaly. 



The laws governing inheritance are for the most part 

 unknown. No one can say why the same peculiarity in 

 diilerent individuals of the same species, or in different 

 species, is sometimes inherited and sometimes not so; why 

 the child often reverts in certain characteristics to its grand- 

 father or grandmother or more remote ancestor; why a 

 peculiarity is often transmitted from one sex to both sexes, 

 or to one sex alone, more commonly but not exclusively to 

 the like sex. It is a fact of some importance to us, that 

 peculiarities appearing in the males of our domestic breeds 

 are often transmitted, .either exclusively or in a much 

 greater degree, to the males alone. A much more im- 

 portant rule, which I think may be trusted, is that, at 

 whatever period of life a peculiarity first appears, it tends 

 to reappear in the offspring at a corresponding age, though 

 sometimes earlier. In many cases this could not be other- 

 wise; thus the inherited peculiarities in the horns of cattle 

 could appear only in the offspring when nearly mature; 

 peculiarities in the silk-worm are known to appear at the 

 corresponding caterpillar or cocoon stage. But hereditary 

 diseases and some other facts make me believe that the 

 rule has a wider extension, and that, when there is no ap- 

 parent reason why a peculiarity should appear at any 

 particular age, yet that it does tend to appear in the off- 

 spring at the same period at which it first appeared in the 

 parent. I believe this rule to be of the highest importance 

 in explaining the laws of embryology. These remarks are 



