Chap. V. LAWS OF VARIATION. 155 



turn to this subject in our chapter on Classification. It 

 would be almost superfluous to adduce evidence in 

 support of the above statement, that specific characters 

 are more variable than generic ; but I have repeatedly 

 noticed in works on natural history, that w r hen an author 

 has remarked with surprise that some important organ 

 or part, which is generally very constant throughout 

 large groups of species, has differed considerably in 

 closely-allied species, that it has, also, been variable in 

 the individuals of some of the species. And this fact 

 shows that a character, which is generally of generic 

 value, when it sinks in value and becomes only of spe- 

 cific value, often becomes variable, though its physiolo- 

 gical importance may remain the same. Something of 

 the same kind applies to monstrosities : at least Is. Geof- 

 froy St. Hilaire seems to entertain no doubt, that the 

 more an organ normally differs in the different species 

 of the same group, the more subject it is to individual 

 anomalies. 



On the ordinary view of each species having been 

 independently created, w r hy should that part of the 

 structure, w 7 hich differs from the same part in other 

 independently-created species of the same genus, be more 

 variable than those parts which are closely alike in the 

 several species? I do not see that any explanation 

 can be given. But on the view of species being only 

 strongly marked and fixed varieties, we might surely 

 expect to find them still often continuing to vary in those 

 parts of their structure which have varied within a mode- 

 rately recent period, and which have thus come to differ. 

 Or to state the case in another manner : — the points in 

 which all the species of a genus resemble each other, 

 and in which they differ from the species of some other 

 genus, are called generic characters ; and these charac- 

 ters in common I attribute to inheritance from a common 



