SELECTION 147 



must. 



tinued for generations to set up any great 

 \XQJI ^Ij^n.; but this, once set up. continues 

 indefinitely. Changed conditions ma n y di- 

 rectly influence the wfopfc n^^^iV^tmn o f 

 the creature or certain parts alone; 



aot, 



system. With respect to the direct action, 

 the _aatnr A ^ tb^ A r ga.mp;fltirm fippfllfi to 



than thflt..f\f 



The effect on the offspring may be definite: 

 e-ff- size may depend UDQQ_the amount of 

 polcnir nnoin n^fl)^Y Q ^ foftd 



f\T sjH'i'Q -^j\H hn.ii* JLIDDTI f* 1 1 rn fi.i'.f'; etc. But 

 indefinite variability is a much commoner 

 result of changed conditions, and has prob- 

 ably played a more important part in the 

 formation of our domestic races. 



and animals will not reproduce in domesti- 

 cation, even though individually vigorous; 

 others, though weak and sickly, breed freely. 

 Hence we need not be surprised at the 

 reproductive system acting irregularly and 

 producing variations. But that variation is 

 not exclusively associated with sexual re- 

 production is demonstrated by the case of 

 plants * ( sporting ' ' through bud- variation. 

 Such cases, moreover, prove that the nature 



