102 Studies in Animal Behavior 



C. became positive when cooled to 6° C. Excep- 

 tional individuals which were positive at 17° to 

 24° became negative at a temperature of 29°. Ma- 

 rine copepods were found by Loeb to be affected in 

 a similar way. Negative specimens of Orchestia 

 agilis I have found to be rendered positive much 

 more quickly if the temperature is raised. The same 

 is true for the water scorpion Ranatra. On the other 

 hand, Dr. Dice observed that in Daphnia pulex low 

 temperature evokes the positive response. And ac- 

 cording to Ewald increase of temperature makes 

 positive larvffi of Balanus negative while decrease 

 of temperature makes negative larvse positive. Dav- 

 enport after discussing the effects of temperature 

 on phototaxis states that "All results may be har- 

 monized in the expression: Diminution of tempera- 

 ture below the normal causes reversal of the normal 

 response ; elevation of temperature to near the maxi- 

 mum accelerates the normal response." Exceptions 

 to this formula are afforded by many of the larvas 

 of Polygordius and by certain species of amphipods, 

 both of which are changed from positive to negative 

 at an unusually high temperature. Many forms 

 which are changed from positive to negative by ex- 

 posure to light are changed more quickly at a higher 

 temperature, but the swarm spores of algffi appar- 

 ently form an exception to this rule. There are 

 many organisms in which the sense of the photo- 

 tactic reaction remains the same, at all intensities of 

 light, and in these cases temperature usually has no 



