The Method of Evolution 41 



kno-\\Ti. When these had been estabhshed, Mendel's law was 

 independently rediscovered long after his death. All honor 

 to the rediscoverers, DeVries, Correns, and Tschermak, 

 that, honoring the all-but-forgotten monk, they called the 

 new-found law Mendel's, rather than their own! 



In Mendel's time little was known about the nature of 

 the reproductive bodies from which new individuals arise, 

 or of how these bodies are produced, or how they differ 

 from the organisms which produce them. These points 

 must be considered briefly. 



An old but ever-recurring question in regard to heredity 

 is this: Does one generation inherit any part of the 

 experience of the previous generation ? In other words, is a 

 character acquired by one generation inherited by the next ? 

 This question, first raised in concrete form by Weismann, 

 has been discussed pro and con for many years, but the con- 

 sensus of scientific opinion at the present time favors Weis- 

 mann's idea that acquired characters are not inherited. 

 In forming a judgment on this question, one fundamental 

 fact should be borne in mind, that in the higher animals 

 body plasm and germ plasm are distinct; that is, the body 

 is distinct from the reproductive cells which it contains, and 

 out of which the next generation is produced. Influences 

 which aft'ect the body have no necessary influence on the 

 germ cells. 



Weismann some years ago demonstrated this experi- 

 mentally for mutilations of the body. When the tails of 

 mice were cut ofl" generation after generation, it was found 

 that young of the mutilated parents had tails as long as other 

 mice. More distinct evidence of the independence of germ 

 plasm and body is furnished by an experiment recently 

 performed by Dr. Phihips and myself. 



