184 MULTIPLE AND RUDIMENTARY [Chap. V. 



Multiple, Rudimentary, and Lowly-organised Structures 



are Variable. 



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

 Hilaire, both with varieties and species, that when any 

 part or organ is repeated many times in the same 

 individual (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 fore^oingr 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 

 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 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 particular shape. Xatural 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. "\Ye shall have to recur to 

 this subject; and I will here only add that their 



