240 



LEE RAYMOND DICE 



The tendency to go to the bottom on increase of light intensity 

 cannot be due to a decrease of locomotor activity as it has been 

 shown by Yerkes (1900) that the locomotor activity increases 

 with increase of light intensity. Neither can it be due to a 

 change of phototaxis because it takes place when the light comes 

 from a horizontal direction. Further, it can be observed that 

 following a great increase of light intensity many of the animals 

 swim directly downwards with the head pointed toward the 

 bottom of the dish. It seems that we have to do here with a 

 change of some sort in the orientation of the animals to the 

 force of gravity. The tendency to move upward following a 

 decrease of intensity is also well marked and must also be due 

 to a change in the reaction of the animals to gravity. 



Exp. 11 



Independence of geotaxis caused by change of light intensity from phototaxis 



February 19, 8.15 A.M., 18 Daphnia pulex from 14 hours in darkness placed in 

 a 29 cm. high jar marked off into five divisions. Exposed to the horizontal light 

 from a 15 ampere electric arc at 50 cm. distance. 



Divisions 

 8.46 A.M. 

 8.47 

 8.50 



Top 

 I 

 

 

 



II 





 

 



III 





 2 



1 



IV 





 8 

 3 



Bottom 



V 



18 



8 



14 



Arc moved to a position above at an angle of 45 degrees 

 8.56 1 



9.00 2 2 5 



9.02 14 



9.05 15 



Arc moved back to horizontal position 

 9.15 1 



9.20 2 



Arc below at angle of 45 degrees 



9.25 4 3 2 



9.30 3 3 4 



9.35 114 6 



9.40 2 5 4 



Arc back to horizontal position 

 9.45 3 3 



10.00 2 13 



10.45 2 2 2 



10.50 

 11.00 

 11.15 

 11.25 



Arc off. 



On light of 40 watt Edison at 50 cm. horizontal 

 14 5 1 



5 4 12 



5 7 3 1 



9 2 11 



17 



9 



13 



12 



17 

 16 



9 

 8 

 6 



7 



12 

 12 

 12 



7 

 6 

 2 

 5 



