LIGHT REACTIONS OF NEWT 33 



as no change of position had taken place at the end of fifteen 

 minutes the interval between observations was changed to five 

 minutes, from observations 7 to 21, after which it was again 

 made three minutes. 



It will be seen from table II that, for the first 18 observa- 

 tions, lasting about one and one-fourth hours, there was very 

 little change in the position of the animals, which lay almost 

 motionless during that time. At the 18th observation the tem- 

 perature of the water had risen to only 7° C, and warm water 

 was carefully added until that in the aquarium was raised to 

 13.5° C. ; the animals soon began to become more active, and 

 after twenty minutes (22nd observation) all were collected in 

 the dark half of the aquarium. From the 22hd observation 

 until the end of the experiment observations were made at 

 intervals of three minutes. It will be seen by table II that 

 the light was changed after the 24th observation, throwing all 

 the animals into the light end; after fifteen minutes all the 

 animals had again collected in the dark region. 



After the 31st observation, when the water of the aquarium 

 had risen to 15° C, warm water was again added until that in 

 the aquarium was raised to 24° C. ; this operation was repeated 

 after the 36th observation and the temperature raised to 33° C. 

 The animals were mostly very active but continued to collect 

 in the dark region, so that after the 43rd observation, when all 

 were in the dark, the ends were reversed, throwing all the 

 animals in the light end. 



After the 50th observation, when ten of the eleven animals 

 were in the dark region, enough water was added to raise the 

 temperature to 36.5° C. ; this caused the animals to become 

 unusually active, to frequently give a squeaking sound, and to 

 come to the surface for air. After this, it will be noticed from 

 the table, there is no longer a tendency to collect in the dark, 

 possibly a slight tendency in the reverse direction. After the 

 59th observation water was again added until that in the aqua- 

 rium was raised to to 38° C. At this temperature the animals 

 acted as just described, but with more vigor. Some of them 

 were so seriously affected that they turned ventral side up and 

 could scarcely right themselves again, and it was evidently im- 

 possible to further increase the temperature without endanger- 

 ing the lives of the animals. 



