LAWS OF VARIATION 203 



greater weight; but until some one will sow, during a 

 score of generations, his kidney-beans so early that 

 a very large proi^ortion are destroyed by frost, and then 

 collect seed from the few survivors, with care to prevent 

 accidental crosses, and then again get seed from these 

 seedlings, with the same precautions, the experiment can- 

 not be said to have been tried. Nor let it be supposed 

 that differences in the constitution of seedling kidney- 

 beans never appear, for an account has been published 

 how much more hardy some seedlings are than others; 

 and of this fact I have myself observed striking instances. 

 On the whole, we may conclude that habit or use and 

 disuse, have, in some cases, played a considerable part 

 in the modification of the constitution and structure; but 

 that the effects have often been largely combined vvith, 

 and sometimes overmastered by, the natural selec ion of 

 innate variations. 



Correlated Variation 



I mean by this expression that the whole organization 

 is so tied together during its growth and development 

 that when slight variations in any one part occur, and 

 are accumulated through natural selection, other parts be- 

 come modified. This is a very important subject, most 

 imperfectly understood, and no doubt wholly different 

 classes of facts may be here easily confounded together. 

 We shall presently see that simple inheritance often gives 

 the false appearance of correlation. One of the most 

 obvious real cases is, that variations of structure arising 

 in the young or larvae naturally tend to affect the struc- 

 ture of the mature animal. The several parts of the 

 body which are homologous, and which, at an early em- 



