REGULATION OF REACTIONS 273 



des Tropfens heriiberzubringen, niederer Temperatur bediir- 

 fen, als wenn sie auf geringere Helligkeitsgrade gestimmt 

 waren. Im ersten Falle wirken Licht und Temperatur 

 sich so zu sagen entgegen, im letzteren so zu sagen 

 gleichsinnig." 



The experimental results of Massart (1891, p. 164) on the 

 flagellate Chromulina confirm those of Strasburger in that 

 a decrease in temperature causes these organisms to become 

 negative to light. Loeb (1905, p. 274) however observed 

 that an increase in place of a decrease in temperature causes 

 a change in the sense of reaction. He says that Polygordius 

 larvae which were strongly negative in a given light inten- 

 sity at 11° became strongly positive when the temperature 

 was lowered to 6°, and negative again when it was raised; 

 that others which were positive at 24° became negative at 

 29°; and that still others positive at 17° became negative 

 at 24°. Loeb claims to have found similar reactions in 

 marine copepods. And Miss Torelle discovered a reversal 

 in reactions in the frog Rana clamata, but here it is again a 

 decrease of intensity that causes negative reactions. She 

 says (1903, p. 487), " A rise in the temperature to 30° C. 

 accelerates the rate of the positive response. A lowering 

 of the temperature to 10° C. produces movements away 

 from the light." Holmes (1905, p. 323) observed similar 

 reactions in Ranatra. He says, '' Raising the temperature 

 tends to accentuate the positive phototaxis in Ranatra and 

 lowering it tends to produce the negative reaction. In 

 several experiments two dishes containing Ranatras were 

 set before a window so as to receive the same amount of 

 light. As the specimens had been previously kept in the 

 dark, they showed a negative reaction. Into one dish warm 

 water was poured raising the temperature from about 20° C. 

 to nearly 30° C. In a few minutes the specimens in the 

 warmer dish became positive, the ones in the cool water 

 still showing a negative phototaxis. Ranatras transferred 

 to the cooler dish soon became negative, while those which 

 were picked up in the same way and dropped back into the 



