LIGHT AND LOCOMOTION IN PHACUS AND EUGLENA. 



2O7 



light when exposed for short periods of time, and that if light 

 has any immediate effect on the rate, it has a retarding effect. 



TABLE II. 



RELATION BETWEEN INTENSITY OF LIGHT AND RATE OF MOVEMENT IN Phacus 

 pleuronectes (POSITIVE INDIVIDUALS). 



Records in the higher intensity obtained first in the first three sets of 

 experiments and last in the rest. 



Each line gives the average rate, for a set of individuals, in a higher 

 and a lower intensity. Each individual represented in the averages was timed 

 twice, once in a higher, and once in a lower intensity. The + signs in the 

 last column indicate a higher rate in higher intensity, the - - signs a lower 

 rate in the higher intensity. 



Englena gracilis. 



The observations on Englena were all made on one species 

 (gracilis}. The specimens used were obtained in laboratory cul- 

 tures containing wheat, a substance which is very favorable for 

 the growth of this species. The methods employed were precisely 

 the same as those employed in the study of Phacus with the fol- 

 lowing exceptions : The observations extended over a wider range 

 of intensities ; they were made under a binocular in place of a 

 compound microscope ; and each individual was tested successively 

 in four different intensities beginning in every case with the low- 

 est, in place of in two different intensities beginning sometimes 

 in the higher and sometimes in the lower; and the course was 0.74 

 mm. in place of 0.34 mm. long. 



