Acquired Modifications Heritable? 113 



institutions, culture, and ideals that have 

 gradually been developed at the expense of 

 much effort, so that the child of today finds 

 himself growing up in an environment that 

 makes success along many lines infinitely easier 

 than for a child of several generations ago. 

 This transmission from generation to generation 

 of the body of social customs and achievements 

 may be termed social heredity, but evidently 

 it is quite distinct from the thing which we 

 ordinarily speak of as heredity — the physi- 

 cal transmission of characters from parent to 

 offspring. 



While it is generally accepted that no envi- 

 ronmental influence can affect the body in such 

 a way as to be transmitted, the environmental 

 influence may directly affect the germ cells. 

 Tower found in experiments on potato beetles 

 that it was possible to produce exceptionally 

 dark animals if the young were reared from the 

 egg in very moist air that was unusually warm, 

 and that, conversely, the animals were very 

 pale if reared in dry cold air. The potato 

 beetle is peculiar in that the germ cells lie 



