Chap. V. 
LAWS OF VAEIATION. 
155 
turn to this subject in our chapter on Classification. It 
would be almost superfiuous to adduce evidence in sup¬ 
port of the above statement, that specific characters are 
more variable than generic; but I have repeatedly 
noticed in works on natural history, that when an au¬ 
thor has remarked with surprise that some important 
organ or part, which is generally very constant through¬ 
out 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. 
Geoffrey 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, why should that part of the 
structure, which 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 explana¬ 
tion 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 moderately recent period, and which have thus 
come to differ. Or to state the case in another man¬ 
ner:—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 charac¬ 
ters ; and these characters in common I attribute to in- 
