No. 575] RESPONSES OF PLANTS AND ANIMALS 651 



was largely based upon the non-inheritance of mutila- 

 tions and the fact that the germ cells of a few organisms 

 are, morphologically, early differentiated from the soma. 

 Turning to its influence upon ideas concerning response, 

 we note that from this viewpoint details of structure 

 were not of fundamental importance unless traceable to 

 the germ plasm. Still, structural details were more im- 

 portant than response, because, with the exception of 

 instincts, responses were believed to occur independently 

 of the germ plasm and hence were of interest only on 

 their own account. Thus the methods used in applying 

 Darwin's theory led to neglect of experimental study of 

 response and culminated in the extreme views of Weis- 

 mann. The germ-plasm theory or the ideas of heredity 

 which are associated with it has dominated zoological 

 thought almost if not quite down to the present day. 2 



4. The Influence of the Study of Response on 

 Peesent-Day Biological Theory 

 One of the most striking developments of recent years 

 has been the discovery that behavior responses are modi- 

 fiable to a high degree. Small traces of reagents reverse 



