ACQUIRED CHARACTERS 175 



of individual differences that are called forth hv the 

 environment. His experiments were carried out on 

 material that was adequate to give a crucial answer 

 to the question involved. In support of Johannsen's 

 conclusion there is an extensive hody of genetic evi- 

 dence which can he interpreted as meaning that 

 while much individual variability is due to minor 

 genetic factors, and this is inherited, some individual 

 variability is due to the environment and this is not 

 inherited. 



Is it possible, then, that Sumner's results were due 

 to chance, in the sense that the two series happened 

 to give the averages shown ? It does not seem prob- 

 able that this w^as so, but we can never be certain 

 until the experiment is re23eated on material that is 

 first made pure for factors involving the length of 

 the parts to be studied. Sumner is himself very cau- 

 tious in his interpretation of his results. He says, 

 "At no time have I declared my results to be proof 

 of, or even evidence for, the inheritance of acquired 

 characters. Indeed, I have insisted that in the pres- 

 ent state of our problems this latter expression has 

 become ho^^elessly obsolete. As regards the various 

 possible interpretations of my own results I have 

 always expressed indecision." 



Castle and Phillips j^erformed an experiment on 

 guinea pigs that w^ould be exj^ected to show the in- 

 fluence of the body on the germ-cells if such effects 

 are 2)ossible. The ovary from a black female was 



