498 



S. O. MAST 



TABLE 4 

 Euglena gracilis (negative and positive). Relation between wave-length and 



stirmdation 



For description of table see legend table 2, p. 492. 



Specimens were taken directly to the laboratory and tested. 

 They were found to be strongly negative and to orient very 

 precisely. 



The results obtained in a series of tests made at this time may 

 be found in table 4, columns 2 to 4. The figures in the second 

 column represent the results of successive tests beginning at the 

 bottom ; those in the other two columns the results of tests made 

 without any regular order of succession. All of these tests were 

 made v/ith the same individuals continuously in the observation 

 aquarium. Toward the close of the experiments many of the 

 individuals became positive, first in the lower illuminations and 

 later also in the higher, and orientation became much less precise, 

 making it impossible to obtain very accurate readings. About 

 an hour later practically all of these individuals were positive 

 and orientation was very precise. A series of tests was made 

 at this time (11.23 to 11.46 a.m.), after which the specimens used 

 were placed in weak light. 



In the afternoon they were again quite as strongly negative as 

 they had been when first brought in and another series of tests 



