210 THE ORIGIN OF SPECIES 



bers, is constant. The same author as well as some 

 botanists have further remarked that multiple parts are 

 extremely liable to vary in structure. As "vegetative 

 repetition," to use Prof. Owen's expression, is a sign of 

 low organization, the foregoing statements accord with 

 the common opinion of naturalists, that beings which 

 stand low in the scale of nature are more variable than 

 those which are higher. I presume that lowness here 

 means that the several parts of the organization have 

 been but little specialized for particular functions; and 

 as long as the same part has to perform diversified work 

 we can perhaps see why it should remain variable, that 

 is, why natural selection should not have preserved or 

 rejected each little deviation of form so carefully as when 

 the part has to serve for some one special purpose. In 

 the same way that a kn.fe which has to cut all sorts of 

 things may be of almost any shape; while a tool for 

 some particular purpose must be of some particular shape. 

 Natural selection, it should never be forgotten, can act 

 solely through and for the advantage of each being. 



Rudimentary parts, as it is generally admitted, are apt 

 to be highly variable. We shall have to recur to this 

 subject; and I will here only add that their variability 

 seems to result from their uselessness, and consequently 

 from natural selection having had no power to check 

 deviations in their structure. 



A Part developed in any Sjjecies in an extraordinary 

 degree or manner, in comioarison with the same Part 

 in allied Species^ tends to he highly variable 



Several years ago I was much struck by a remark, to 

 the above effect, made by Mr. Waterhouse, Professor 



I 



