Harper, Reactions of Peric/uvta. 587 



qiient except under conditions of strong and sudden illumination. 



Physiological state is of unusual importance in connection with 



receptivity to light. 



9. An electrical stimulus when suddenly introduced produces 



shrinking, when introduced gradually may produce only turning. 



Northwestern University, Zoologicax Laboratory. 

 April 10, 1909. 



LITERATURE LIST. 

 Adams, George P. 



1903. On the negative aud positive pliototropism of tlie earthworm, 

 Allolobophora foetida (Sav.), as determined by light of dif- 

 ferent intensities. Am, Jour. Physiol., vol. 9. 

 Harper, E. H. 



1905. Reactions to light and mechanical stimuli in the earthworm, 



Perichaeta bermudensis (Beddard). Biol. Bui., vol. 10, pp. 

 17-34. 

 Jennings, H. S. 



1906. Factors determining direction and character of movement in 



the earthworm. Jour, of Exp. ZooL, vol. 3, no. 3, pp. 435-455. 

 Loeb, J. 'i 



1907. Concerning the theory of tropisms. Jour, of Exp. ZooL, vol. 4, 



no. 1, Feb., '07, pp. 151-156. 

 Torrey, Harry Beal. 



1907. The method of trial and the tropism hypothesis. Science, N. S., 

 vol. 26, no. 602, Sept. 6, pp. 313-323. 

 Whitman, C. O. 



1899. Animal behavior. Woods Hole Lectures. Boston, 1899. 



