16 VARIATION TTNDEK DOMESTICATION. [Chap. I. 



reappear in trie offspring at a corresponding age, 

 though sometimes earlier. In many cases 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 appear at the corresponding caterpillar or 

 cocoon stage. But hereditary diseases and some other 

 facts make me believe that the rule has a wider exten- 

 sion, 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 confined to the first appearance, of the pe- 

 culiarity, and not to the primary cause which may have 

 acted on the ovules or on the male element ; in nearly 

 the same mauner 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 boldy 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 



