IV 



Can We Experimentally Change the Hereditary Charac- 

 ters? Heredity of Environmental Effects. Heredity and 

 Variation in Bacteria and Similar Organisms. 



have seen that in Difflugia hereditary variations 

 arise even when the organisms are all kept as nearly 

 as possible under the same conditions. Thus from a single 

 strain, all derived by fission from one ancestor, many strains 

 arise, diverse in their hereditary characters. 



Can such changes be brought about by the action of 

 special conditions in the environment? Can we experimen- 

 tally produce such hereditary changes? Have some of the 

 diverse strains existing in nature been produced by action 

 of the environment? We saw in our introductory lecture 

 that structural characters produced in the body of Protozoa 

 during the lifetime are not inherited any more directly than 

 are such characters in higher organisms. To be inherited, 

 the acquired structures must be produced anew by the off- 

 spring, and for most acquired characters this does not 

 occur; the offspring are produced in the same state that 

 the parents were. But there still remains the question 

 whether the organisms cannot be so altered that in the 

 succeeding generations characters will be produced that are 

 different from those produced in the earlier generations. 



1. Bacteria 



Most of the significant work bearing on this question has 

 been done on the bacteria, and on other organisms that 



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