184 MULTIPLE AND RUDIMENTARY. [Chap. V. 



Multiple, Rudimentary, and Lowly-organised Structures 

 are Variable. 



It seems to be a rule, as remarked by Is. Geoffry St. 

 Hilaire, both with varieties and species, that when any 

 part or organ is repeated many times in the same in- 

 dividual (as the vertebrae in snakes, and the stamens 

 in polyandrous flowers) the number is variable; whereas 

 the same part or organ, when it occurs in lesser numbers, 

 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 organisa- 

 tion, 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 organisation have been but 

 little specialised 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 re- 

 jected 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 knife which has to cut all 

 sorts of things may be of almost any shape; whilst a 

 tool for some particular purpose must be of some par- 

 ticular shape. Natural selection, it should never be 

 forgotten, can act solely through and for the advantage 

 of each being. 



Eudimentary 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 varia- 



