338 HEREDITY AND ENVIRONMENT 



contain no adult characteristics, it seems very 

 improbable that any peculiarity of environ- 

 ment whether of nutrition, use, disuse or in- 

 jury, which brings about certain peculiarities 

 of developed characters in the adult, could so 

 change the structure of the germ cells as to 

 cause them to produce this same character in 

 subsequent generations in the absence of its 

 extrinsic cause. How, for example, could de- 

 fective nutrition, which leads to the produc- 

 tion of rickets, affect the germ cells, which 

 contain no bones, so as to produce rickets in 

 subsequent generations, although well nour- 

 ished? Or, how could overexertion, leading to 

 hypertrophy of the heart, so affect the future 

 germ cells that they, in turn, would produce 

 hypertrophied hearts in the absence of over- 

 exertion, seeing that germ cells have no hearts ? 

 Or how could the loss or injury of eyes or 

 teeth or legs lead to the absence or weakened 

 development of these organs in future genera- 

 tions, seeing that inheritance must be through 

 germ cells which possess none of these 

 structures? 



But, apart from these general objections to 



