3/0 'Journal of Comparative Neurology and Psychology. 



years ago, while I was connected with Clark University of Atlanta, 

 Georgia. They were continued at the University of Chicago dur- 

 ing the summer and autumn of 1906 and the winter of 1907. I 

 take this opportunity to express my gratitude to the University of 

 Chicago for the scholarship privileges granted me, without which 

 the publication of this contribution would have been much delayed. 

 I also wish to acknowledge my indebtedness to the members of 

 the Zoological and Psychological Departments for their encourage- 

 ment, and especially to Dr. C. M. Child for his sustained interest 

 in my work and for suggestive criticisms, and to Dr. F. R. Lillie 

 for his assistance in revising the manuscript. 



I. EXPERIMENTS ON TROPISMS. 



Bethe's insistence ('98, '02), in spite of the opposition of 

 Wasmann ('98, '99, '01), Buttel-Reepen ('00) and Forel ('01), 

 that ants are merely reflex machines, led me to plan the series of 

 experiments discussed in this section. The purpose of the experi- 

 ments w^as to see what role, if any, tropisms play in the homing of 

 ants. These homing activities were selected for study because 

 they could easily be investigated under controlled conditions suffi- 

 ciently simple to yield reliable results. Only such forms of stimuli 

 were investigated as might possibly influence the normal activities 

 of the ants. 



Heliotropism. — "The essential feature of heliotropic reaction" 

 says LoEB ('06, p. 124), "consists in the fact that the light auto- 

 matically puts the plant or animal (Eudendrium, Spirographis) 

 into such a position that the axis of symmetry of the body or organ, 

 falls in the direction of the rays of light." Light may play an 

 important role in the life of an organism without that creature 

 being heliotropic. "Heliotropism (Loeb '06, p. 135) covers only 

 those cases where the turning to the light is compulsory and irre- 

 sistible, and is brought about automatically or mechanically by the 

 light itself." 



A large number of experiments were made to see what part helio- 

 tropism as defined by Loeb plays in the home-going of ants. In 

 each experiment one or more cardboard stages and inclines were 

 used. Illumination was furnished, in some cases by diffuse day- 

 light through a window, and in others by a 16 c. p. incandescent 

 light. For each experiment a new cardboard stage and inclines 



