Production of Inherited Variations 201 



to this the fact that in higher organisms the germinal mate- 

 rial is commonly hidden deeply within a great mass of body 

 cells, by which its surroundings are kept uniform and it is 

 protected from marked changes of all sorts, and it becomes 

 more intelligible why in higher organisms inherited changes 

 due to the action of the environment are much less commonly 

 observed than general theory might lead us to expect. In 

 the bacteria and Protozoa the germinal material is not pro- 

 tected by a great mass of body cells, but is more directly 

 exposed to the action of environmental agents, so that in 

 these, heritable results of environmental action are better 

 known. 



When we examine the experimental evidence on this matter 

 in higher organisms, we find that scientific opinion looks 

 upon it as being in a somewhat less satisfactory condition 

 than appeared to be the case a few years ago. Cases had 

 been described in which the inheritance of the action of the 

 environment on the germ cells appeared clear ; and the evi- 

 dence on these particular cases has not altered. But the 

 lack of further confirmation, of other instances ; the failure 

 of other tests under similar conditions, has shaken the 

 opinion of most students of biology as to the conclusiveness 

 of the evidence that had been given, and has made them 

 inclined to wait for further evidence before accepting the 

 principles of action involved. No subject in biology is more 

 in need of further work than this one. 



The principal evidence for actual modification of the 

 germ cells by the environment in such a way as to cause the 

 appearance in the body of new hereditary characters has 

 come perhaps from the work of Standfuss (1906) and 

 Fischer (1907); of Tower (1906); of Kammerer (1913), 

 and of Stockard (1913); these at least are typical. It is 

 not our present task to give an account of these researches, 



