208 



S. O. MAST AND MARY COVER. 



A summary of the results obtained is presented in Table III. 



TABLE III. 



RELATION BETWEEN RATE OF LOCOMOTION AND LUMINOUS INTENSITY IN Euglena 



gracilis. 



Each individual was timed successively, once in each of the intensities 

 indicated, beginning in every instance with the lowest. The time presented is, 

 in every case, the average of that required for each of the individuals indi- 

 cated to travel once over the course in the illumination indicated. 



This table shows that in intensities ranging in the one 'set of ex- 

 periments from 286 m.c. to 2106 m.c. and in the other from 84 m.c. 

 to 853 m.c. there is remarkably little difference in the rate of 

 locomotion, the difference between the rate in the lowest intensity 

 and that in the highest intensity being only .0276 -|- mm. per 

 second in the one set and .0298 -|- mm. in the other. It shows 

 that, in the time it takes Euglena to travel 10 mm. in the lowest 

 intensity it would travel only a little more than 10.2 mm. in the 

 highest intensity, and that the lowest rate is not consistently in 

 the lowest intensity. 



The results obtained consequently indicate that light in certain 

 intensities slightly accelerates locomotion in Euglena, and slightly 

 retards it in Phacus. Orientation cannot, however, be due to the 

 effect on the rate of locomotion of difference in the illumination 



