2 4 '2 



LEE RAYMOND DICE 



GEOTAXIS IN RELATION TO TEMPERATURE 



On heating Daphnia pulex in the dark to a temperature of 

 about 25° C. there is a strong tendency for the animals to go 

 to the bottom of the dish (Exp. 13). On cooling them to a 

 temperature of about 15° C. there is a tendency for them to go 

 to the surface (Exp. 14). The position of these animals kept in the 

 dark was determined by turning on a weak light and taking the 

 observation before the position of the animals could change. 

 The tendency to go down on heating cannot be due to the effect 

 of temperature on the locomotor activity, because it will be 

 shown in a later section that increase of temperature causes an 

 increase of locomotor activity which would tend to cause the 

 animals to move upwards. Neither can this tendency be due 

 to any effect of light because the tendency is present in the 

 complete absence of light. Seemingly it is due to a change in 

 the orientation of the animals with respect to gravity. We may 

 then suppose that the tendency to move upward on cooling is 

 also due to a change in the relation of the animals to the force 

 of gravity. In horizontal light the same effect of temperature 

 on geotaxis is found (Exp. 15). 



Exp. 13 



Positive geotaxis caused by heating 



March 19, 8 A.M., 10 Daphnia pulex from 14 hours in darkness placed in a 29 

 cm. high jar marked off into three divisions. Kept in complete darkness except 

 when making observations. Temperature 21° C. 



