158 S. O. MAST 



Thus it was found that while rapid movement of a 500 c.p. lamp 

 from 40 cm. to 50 cm. from the organisms produced activating 

 responses, slow movement from 40 cm. to 400 cm. produced no 

 responses. One experiment is particularly interesting in this 

 connection. Under the binocular, twelve tadpoles of Amarou- 

 cium pellucidum all in the field at the same time were observed 

 resting in contact with the surface film. They were at this 

 time in a horizontal beam of light of 3000 m.c. A shadow was 

 thrown upon these specimens by very rapidly passing the hand 

 through the beam. Nine of the twelve immediately responded 

 by becoming active, but all of them soon came to rest again in 

 contact with the surface film. The lamp was now in the course 

 of one-half minute moved from 40 cm. to 400 cm. from the 

 organisms, reducing the intensity from 3000 m.c. to about 30 

 m.c. There was no response in any of the tadpoles. The hand 

 was then slowly passed through the beam. One tadpole 

 became active. Five minutes later this was repeated, but no 

 response was obtained. The light in the beam was then inter- 

 cepted for 20 hm.; again no response was obtained. The lamp 

 was now moved so as again to increase the light to 3000 m.c. 

 and the open hand with fingers spread passed very rapidly 

 through the beam. Nine of the twelve specimens became active. 

 Similar results were obtained in obervations in front of a window 

 provided with an opaque shutter. In reducing the illumina- 

 tion by closing the shutter activating responses could readily be 

 induced by rapid movements through 10 to 15 cm., while slow 

 movement produced no responses even when the shutter was 

 entirely closed, resulting in total darkness excepting a weak ruby 

 light which was practically neutral in its stimulating effect. (This 

 light was commonly used throughout all of these experiments 

 in making observations in low illuminations.) It is thus evident 

 that the stimulating efficiency of reduction in illumination 

 depends markedly upon the time-rate of reduction. 



Amaroucium tadpoles, as previously stated, may be photo- 

 positive or photonegative. In Euglena and various other 

 similar organisms in which a reversion of this sort occurs it has 

 been found that photopositive specimens respond in a certain 



