23 VARIATION Chap. I. 



In many cases this could not be otherwise : thus the inherited 

 pocuharities in tlie horns of cattle could appear only in the 

 oflsprini^ when nearly mature ; peculiarities in the silkworm 

 are known to appear at the corrcsjoondinf^ caterpillar or cocoon 

 staple. But hereditary diseases and some other facts make mc 

 believe that the rule has a Avider extension, and that, when 

 there is no apparent reason why a peculiarity should appear at 

 any particular ai^e, yet that it does tend to appear in the off- 

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

 ent. I believe this rule to be of the hig-hest importance in 

 explaining- the laws of embryology. These remarks are of 

 course confined to the first appearance of the peculiarity, and 

 not to its primary cause, which may have acted on the ovules 

 or on the male element ; in nearly the same manner as in the 

 ofi'spring- from a short-horned cow by a long-horned bull, the 

 greater length of horn, though appearing late in life, is clearly 

 due to the male element. 



Having alluded to the sul)ject of reversion, I may here refer 

 to a statement often made by naturalists — namely, that our 

 domestic varieties, "when rim Avild, gradually but invariably re- 

 vert 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 endeavored to 

 discover on what decisive facts the above statement has so 

 often and so boldly been made. There Avould be great difli- 

 cidiy 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 state. In many cases we do not know 

 Avhat the aboriginal stock was, and so could not tell whether 

 or not nearly perfect reversion had ensued. It Avould be ne- 

 cessary, in order to prevent the effects of intercrossing", that 

 only a single variety should have been turned loose in its new 

 home. Nevertheless, as our varieties certainly do occasionally 

 i-evert in some of their characters to ancestral forms, it seems 

 to mc not improbable, that, if we could succeed in naturalizing, 

 or were to cultivate, duringmany generations, the several races, 

 for instance, of the cabbage, in very poor soil (in which case, 

 however, some effect would have to 1)C attributed to the definite 

 action of the poor soil), they would to a large extent, or 

 even wholly, revert to the wild aboriginal stock. Whether or 

 not the experiment would succeed, is not of great imjiortance 

 for our line of argument ; for by the experiment itself the con- 

 ditions of life are chanixed. If it couUl be sliown that our do 



