THE 



AMERICAN NATURALIST 



Vol. XLIV January, 1910 No. 517 



THE REAPPEAR A XCE IX THE OFFSPRING OF 

 ARTIFICIALLY PRODUCED PARENTAL 

 MODIFICATIONS 1 



DR. FRANCIS B. SUMNER 

 Wood's Hole, Mass. 



In a recent paper 2 I have described a series of experi- 

 ments conducted during the past few years upon white 

 mice. I have there shown that large enough differences 

 of temperature, operating throughout the period of 

 growth, bring about considerable, and in some cases 

 quite obvious, differences in the length of peripheral 

 parts (tail, foot and ear), and probably changes in the 

 quantity of hair as well. The peripheral parts were 

 found to be longer in the warm-room lots (12 to more 

 than 30 per cent, longer, in the case of the tail) ; the 

 amount of hair, on the contrary, was less. It was pointed 

 out, furthermore, that differences of precisely this sort 

 have long been known to distinguish northern from 

 southern races of mammals. 



The question of most vital interest was not, however, 

 touched upon in the earlier paper, although it has fur- 

 nished my real motive for pursuing these experiments 

 throughout. Are these modifications purely transitory, 



