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k 



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1 



^t two .: 



k 



use of 



as it 



^^te and fo 

 made 



^ °^ Natural Se 

 ghiyi 



ttf 



)rou 



'^ accoii- 



^i^Hy clear k 

 and particular,?: 

 t the direct 



aj: 



as It 



ly strong ID 



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4 



, and vol. "• 



■thepOS5>« .y 



■0 *e M- ' , 



:he-0n8»>:= 

 tions- ^ 



the 



TI/£ BEGINNINGS OF LIFE 



579 



its bearings upon the shapes and modes of growth 

 of plants of different kinds^ and is applicable even 

 to their most minute details of structure. Amongst 

 animals, however, the indirect influence of change in 

 external conditions (that which acts by inducing modi- 

 fied function, or ^use and disuse') is also frequently 

 recognizable ^ — this mode of operation being favoured 



L 



. by the fact that the functions of animals are more 

 differentiated than those of plants. As Mr. Spencer says^ 

 in order that ^ a new external action may be met by a 

 new internal action, it is needful that it shall either con- 

 tinuously or frequently be borne by the individuals of the 

 species, without killing or injuring them 2/ If the new 

 influence act immediately upon the nutrition of the 

 organism in a way which we are unable to explain (as is 

 so frequently the case amongst plants), we regard it as 



)ns of life are 1(1 



ic variability ain'i 

 the ephemeroir 



ind side by sides a case of the direct influence of change in conditions; 



).cquals, yet 



whilst if the change acts (as is frequently, though by 



tions ^. The evil' no means invariably, the cas 



amongst animals) in 



the direct influ* more slowly bringing about some obvious difference 



in function, then the difference of function is gene- 

 rally credited with bringing about the variation, and 

 the action of the change in conditions is at least said 

 to be « indirect.' Changes brought about by ^ use and 

 disuse,' in reality, therefore, belong to the same cate- 

 gory as those other changes which are said to be 



' Principles of Biology,' vol. i. p. 439 

 Loc. cit., vol. i. p. 442. 



P p 2 



\ 



