TRANSFORMATION OF HELIOTROPIO ANIMALS 275 
other vessels in which the temperature had not been changed, 
all the animals had remained, without exception, negatively 
heliotropic. I took pains to keep the temperature in the 
vessel itself uniform throughout. 
Later, when I allowed the temperature in the cooled dish 
to rise again, the animals gradually became negatively 
heliotropic as soon as the temperature reached 6° C. and 
above. 
It could be shown that the absolute height of the tempera- 
ture, and not the sudden fall in the temperature alone 
made the animals positively heliotropic. When I removed 
negatively heliotropic animals from water having a tempera- 
ture of 23° C., and brought them suddenly into water hav- 
ing a temperature of 13° C., they remained negative even 
when I waited as long as an hour; while, when the tempera- 
ture sank as low as 7° C., the animals became positively 
heliotropic in a few minutes. When the temperature was 
lower than 6° C., the animals remained positively helio- 
tropic as long as the temperature remained as low as this (in 
some experiments this was for two hours). The temperature 
at which the animals become positive is, of course, not ab- 
solutely the same in all experiments. I have repeated the 
experiments with many modifications, and have always found 
that when cooled below +7° C. all, or almost all, the animals 
became positively heliotropic. 
A few observations on the behavior of these animals at 
low temperatures may perhaps be of interest. The positive- 
ness of the animals at + 4° C. was greater than the positive- 
ness of the animals at +7° C., the oscillations from the 
straight line were smaller, and their movements more ener- 
getic—a fact which I had not anticipated. I still observed 
positively heliotropic reactions at a temperature of +0.4° C. 
The reaction to light ceased at —0.5° C., although the 
animals still moved, and at — 2° C. the animals passed into 
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