THEORIES OF EVOLUTION 157 



In 1893 there was published an English translation 

 of his famous book The Germ-Plasm which stimulated 

 so much discussion among biologists. This sets 

 forth his theory of heredity. For many years Weis- 

 mann was a professor in the University of Freiburg, 

 and his lectures on the evolution theory were de- 

 servedly famous and well attended. The best 

 exposition in English of his theory is The Evolution 

 Theory, published in two volumes in 1904. In the 

 preface he says: "I make this attempt to sum up and 

 present as a harmonious whole the theories which for 

 forty years I have been gradually building up on the 

 basis of the legacy of the great workers of the past, 

 and on the results of my own investigations and 

 those of my fellow-workers." 



Since we may assume that there has been unbroken 

 continuity of the germ-plasm from the beginning, we 

 may also assume that its organization has become 

 very complex. Protoplasm is impressionable, re- 

 sponding to various forms of stimuli and undergoing 

 modifications in response to environmental influences. 

 These subtle changes occurring within the proto- 

 plasm affects its organization, and, in the long run, 

 it is the summation of experience that determines 

 what a particular mass of protoplasm shall be and 



