LIGHT AND LOCOMOTION IN PHACUS AND EUGLENA. 2OQ 



of the sensitive tissue in different positions on the spiral course 

 of these organisms, as is demanded by the De Candolle-Verworn 

 theory applied to asymmetrical organisms by Torrey, Bancroft 

 and others, for the effect on the rate is, even under the most 

 favorable condition, so small that if orientation were dependent 

 upon this, it would require much longer than it actually does ; and 

 moreover, orientation occurs under luminous conditions in which 

 an increase or a decrease in intensity does not appear to ap- 

 preciably effect the rate of locomotion. 



The facts presented above have no bearing on the question as 

 to the effect of light on the rate of locomotion in long exposures. 

 All of the evidence obtained by various investigators in reference 

 to this indicates that organisms like Phacus and Euglena come to 

 rest if they are subjected for long periods to low illumination or 

 darkness. This is probably owing to the effect of light on physio- 

 logical processes (e.g., photosynthesis) which in turn affect the 

 activity of the organisms. 



LITERATURE CITED. 

 Bancroft, F. W. 



'13 Heliotropism, Differential Sensibility, and Galvahotropism in Euglena. 



,--Jour. Exp. Zool., Vol. 15, pp. 383-428. 

 De Candolle, A. P. 



'32 Physiologic vegetale. Paris. 

 Loeb, J. .' 



'18 Forced Movements, Tropisms, and Animal Conduct. Philadelphia. 



20'9 pp. 

 Torrey, H. B. 



'13 Trials and Tropisms. Science, Vol. 37, 873-876. 

 Verworn, M. 



'08 (First ed. 1894) Allegemeine Physiologic. Jena, 742 S. 



