58 LIGHT AND THE BEHAVIOR OF ORGANISMS 



rect effect through a direct reflex arc as suggested by Loeb, 

 or is the whole organism more or less involved in the re- 

 action in accord with the ideas of Jennings and Holmes? 

 If orientation is direct, precisely what movements are 

 involved in the process? Are the avoiding reactions due 

 to differential response to localized stimulation, as held by 

 some, or is the direction of turning in such reactions abso- 

 lutely determined by the structure and physiological state 

 of the organism? Are the reactions to light in general 

 adaptive and modifiable in accord with Jennings' analysis, 

 or are they fixed and forced and unequivocally controlled 

 by the external agent in accord with Loeb's ideas? Are 

 the more refrangible rays most active in stimulating all 

 organisms as claimed by Loeb and Davenport, or are some 

 organisms stimulated more by waves of a certain length, 

 and others by waves of a different length as claimed by 

 Verworn and Nagel? These questions and others we shall 

 attempt to answer in the following pages. 



