16 VARIATION UNDER DOMESTICATION. [Chap. 1. 



reappear in the offspring at a corresponding age, though 

 sometimes earlier. In many oases this could not be 

 otherwise; thus the inherited peculiarities in the horns 

 of cattle could appear only in the offspring when nearly 

 mature; peculiarities in the silkworm are known to ap- 

 pear 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 apparent reason why a peculiarity 

 should appear at any particular age, yet that it does 

 tend to appear in the offspring 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 of course con- 

 fined to the first appearance of the peculiarity, and not 

 to the primary cause which may have acted on the 

 ovules or on the male element; in nearly the same 

 manner as the increased length of the horns in the 

 offspring from a short-horned cow by a long-horned 

 bull, though appearing late in life, is clearly due to the 

 male element. 



Having alluded to the subject of reversion, I may 

 here refer to a statement often made by naturalists — 

 namely, that our domestic varieties, when run wild, 

 gradually but invariably revert in character to their 

 aboriginal stocks. ^Hence it has been argued that no 

 deductions can be drawn from domestic races to species 

 in a state of nature. I have in vain endeavoured to 

 discover on what decisive facts the above statement 

 has so often and so boldly been made. There would be 

 great difficulty in proving its truth: we may safely 

 conclude that very many of the most strongly marked 

 domestic varieties could not possibly live in a wild 



