2O6 S. O. MAST AND MARY COVER. 



I. includes, for each of 20 individuals, two records, one taken in 

 higher and the other in lower intensity. In each case the record 

 for the lower intensity w r as obtained first. That is, the rate of 

 locomotion for a given individual was ascertained in the lower 

 intensity, then the light was moved nearer to the microscope and 

 the rate ascertained for the same individual in the higher intensity. 

 After the two readings had been obtained for one individual, the 

 light was moved to its original position, another individual timed 

 in the same way, and so on until the rates for 20 or more indi- 

 viduals were recorded. 



By referring to Table I., it will be seen that the rate of loComo- 

 tion of any one individual in the lower intensity was practically 

 the same as it was in the higher intensity. The table shows that 

 tlie average time required to travel .34 mm. was 5.63 sec. in the 

 lower and 5.69 sec. in the higher intensity, indicating a slightly 

 higher rate in the lower intensity. The difference referred to is, 

 however, only .06 of a sec. This is probably within the limits of 

 error, since a further examination of the table shows that the rate 

 was not consistently higher in the lower intensity, 9 individuals 

 traveling faster in the higher intensity, 8 slower and 3 at the same 

 rate in the two intensities. That is, the rate varied about as fre- 

 quently in one direction as in the other. This shows that there is, 

 in Phacns, practically no difference in the rate of locomotion in lu- 

 minous intensities varying from 1023 m.c. to 4128 m.c., and it 

 indicates that locomotion is not to any considerable extent im- 

 mediately related with the intensity of the illumination. 



A summary of the results obtained in all of the observations 

 made are presented in Table II. By referring to this table it 

 will be seen that the rate of locomotion was on the average slightly 

 higher in the lower intensities than it was in the higher, the aver- 

 age time required to travel 0.34 mm. being 6.002 seconds in the 

 former and 6.134 seconds in the latter. The difference is, how- 

 ever, so small and inconsistent, being in favor of the higher il- 

 lumination in two out of the nine sets of tests, that its significance 

 is questionable. These results support the conclusions formu- 

 lated above. They show that the rate of locomotion in Phacus 

 is within wide ranges, practically independent of the intensity ot 



