MOTOR RESPONSES 



291 



intensity is rapidly increased, it stops suddenly and then deflects the 

 anterior end sharply to one side. If the intensity is slowly increased, or if 

 it is decreased, there is no response. The entire organism is sensitive to 



0.1 TTL jri. 



i 



Figure 103- Camera drawings illustrating the response of Peranema to contact or to 

 rapid increase in luminous intensity. Al, normal locomotion ; 2, immediately after re- 

 sponse; 3, 4, recovery from response; B, response to contact with grain of sand, o, and 

 recovery. Note that response results in a change in the direction of motion of approxi- 

 mately 90 degrees. (Mast, 1912.) 



light, but the flagellum is most sensitive and the posterior end least sen- 

 sitive (Shettles, 1937). 



Dark adaptation. — Mast and Hawk (1936) demonstrated that if 

 light-adapted peranemae are subjected to darkness, the time required in 

 light of 2,000 meter-candles to induce the response decreases from 30.95 

 seconds after 15 minutes in darkness to a minimum of 4.54 seconds after 

 one hour in darkness, then increases to a maximum of 63.46 seconds 



