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CHAPTER X. 



USE OR DISUSE OF PARTS AND ADAPTATIONS 

 OF ORGANS. 



ACCORDING to Darwin, the use and disuse 

 of parts, and the habits due thereto, with 

 their consequences, are transmitted by 

 parents to their offspring, and thus what 

 were at first slight differences accumulated 

 from generation to generation until they 

 ultimately become specific variations ; and 

 conversely, by disuse organs once perfect 

 degenerate, and come to be represented in 

 some cases only by fragmentary remains. 



It is not questioned that differences in 

 expression of type, limited in extent, do 

 arise from various causes. Every organ 

 has its allotted share of the life -force of 

 an animal, and with normal use develops 

 normally. Experience teaches that an organ 

 may be developed abnormally by excessive 

 use apparently by transfer to it of part of 

 the life-force of some other part of the or- 



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