588 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



at the time when the gene sets undergo marked changes, suggest the pos- 

 sibility that gene mutations may be involved in these processes. However, the 

 strictly adaptive natures of such modifications, as well as the fact that after 

 all they are, as a rule, not permanent, makes it more probable that they are not 

 due to genetic changes ; they would not therefore represent changes in the or- 

 ganismal differentials. 



From all these observations it may be concluded that there is no evidence 

 that in higher organisms an actual change in the constitution of the organismal 

 differentials occurs ; but changes may take place in the quantity of differentials 

 which are produced and in the character of the reaction against these differ- 

 entials. On the other hand, in certain unicellular organisms, in which the 

 criteria used for the definition of organismal differentials in higher organisms 

 cannot be applied, changes have been observed, which in certain respects may 

 perhaps correspond to modifications of the organismal differentials. 





