i ' 



h 



I 



,t 



418 



CONCLUDING REMARKS 



Chap. XXVIII 



* 



t 



liable to slight deviations of structure and 



species 



g under 



their 



natural conditions, and as wiclely- 

 g species vary more than those which inhabit restricted 

 we may infer that variability mainly depends on changed 



conditions of life. We must not overlool 



effects of 



qual combination of the characters derived from both parent 



former progenito 



an 



especial tendency 

 less impotent, as si 



ender the 



Changed conditions 

 reproductive organs 



the chapter devoted to this 



and these organs consequently often fail to transmit faith 



fully the parental characters, 

 directly and definitely on the ( 



all the 



duals of 



Changed conditions also act 



anisation, so that all or nearly 



same species thus exposed become 



this or that part is 



In most 



s 



modified in the same manner; but why this 



especially affected we can seldom or never say 



however, of the direct action of changed conditions, independ 



ently of the indirect variability caus< 



d 



the 



eproc 



& 



benm* affected, indefinite modifications are the 



ly the same 



exposur 



the absorpt 



of the same poison affects different individuals in various way 



We ha\ 



ipect that an habitual 



of highly 



food, or an excess relatively to the wear and tear of 



organisation from 

 ability. When w< 



powerful exciting cause of 



the symmetrical and complex 



aused by a minute atom of the poison of 



may bel 



that 



changes in the chemical 



of 



the sap or blood would lead to 



y 



modificat 



of 



The increased use of a muscle with its various attached par 



and the increased activity of a gland or other organ, lead 



ased development. Disu 



has 



a 



7 



effect 



With 



domesticated productions organs sometimes become rudimentary 

 through abortion ; but we have no reason to suppose that this 



has ever followed from mere disuse. With natural species 



ir to have been rendered r 



■y, many 



appe 



mentary through disuse, aided by the principle of the economy 

 of growth, and by the hypothetical principle discussed in the 



chapter, namely, the final destruction of the 



mules of 



useless parts. This differ 



ay 



be partly 



. 



v 



.'.' 



• 



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