292 



MOTOR RESPONSES 



after 6 hours in darkness, and then remains nearly constant. As the time 

 in darkness increases, the sensitivity to hght rapidly increases to a maxi- 

 mum, then decreases to a minimum, before it becomes constant (Fig. 

 104). 



so 





■30 



O 

 K 

 U 

 •^20 



6 8/0 



TIME IN DARk^NCSS IN HOURS 



12 



14 



24 



Figure 104. Graph showing the effect of dark-adaptation on sensitivity to light in 

 Peranema trichophorum. Each point on the curve, except the last two, represents the 

 average reaction time for from fifteen to seventeen tests. (After Mast and Hawk, 1936.) 



Light adaptation. — Shettles (1937, 1938) made a much more exten- 

 sive and thorough investigation of this response. He confirmed the con- 

 clusions reached by Mast and Hawk (1936). A brief summary of other 

 results obtained, and the conclusions reached, follows: 



If dark-adapted peranemae are subjected to light, their sensitivity to 

 light increases rapidly to a maximum, then decreases considerably, after 

 which it remains nearly constant (Fig 105). The reaction time consists 



