The Reactions of Planarians to Light 



109 



first to come to rest and those least affected by fatigue continue 



longest in motion 



TABLE XXIII 



The average generic and specific dijference in fatigue 





Generic differences 



Specific differences 





Dendro- 

 coelum 



Phagocata ' Planaria 



Planaria 

 maculata 



Planaria 



gonocephala 



Percentage of change in rate of 













the fourth trial as compared 

















+ 9-5 



-9 



-13 



-5 



Percentage of change in time 





required to leave a unit circle 













of the last four as compared 













■with the first four of twelve 















-33 



-10 



-15.8 



~ 2 3 



-8. 7 



Average percentage of fatigue 



— 22 



—0.25 



— 12.4 



-18 



-6.8 



Total number of comparisons 



30 



20 



40 



20 



20 



Responses to Changes in Intensity'. When worms in non-direc- 

 tive light pass from a given intensity to one l\ times as great, 

 decided differences appear in their behavior, the generic differences 

 being plainly of wider range than the specific. 



table xxrv 



Average differences in response at the critical line separating two areas of non-directive light of which 

 one (82.50 cm.) is approximately 2-h times as great as the other (33.16 cm.) 



Generic differences 



Dendro- 

 coelum 



Number of observations 



Percentage of responses 



Percentage of failures to re- 

 spond 



45 



17 



Phagocata 



202 



37 



63 



Planaria 



206 



52.5 



47-5 



Specific differences 



Planaria 

 maculata 



5° 



55 



45 



Planaria 



gonocephala 



156 



5° 



5° 



In this table Dendroccelum is shown to respond in only 17 per 

 cent of its passages across the critical line separating the two dif- 

 ferent intensities of light, while Phagocata responds in 37 per cent 



