276 STUDIES IN GENERAL PHYSIOLOGY 
cold rigor. As the animals are exceedingly small, it is 
reasonable to assume that their temperature was almost 
identical with that of the sea-water in which they were con- 
tained. 
Positively heliotropic Polygordius larve can easily be 
made negatively heliotropic through an increase in tempera- 
ture. I put some animals, which at the room temperature 
of + 24° C. had all become positively heliotropic, into a 
dish, and put the dish, as usual, into another glass vessel of 
larger size. At 10:45 a.m. warm water was poured into the 
outer vessel. At 10:52 the temperatuze of the dish con- 
taining the animals was 25.5° C., and all the animals were 
still positively heliotropic. Five minutes later, when the 
temperature had reached 29° C., all the animals became 
negatively heliotropic. The reaction continued the same 
until 34° C., when the animals no longer reacted to light. 
In another experiment the animals were positively helio- 
tropic at the room temperature of 17° C. When I raised 
the temperature to 24° C., in the same way, as before, the 
animals became negatively heliotropic, and their negative- 
ness increased at first with an increase in temperature. Just 
as it was possible every time to make negatively heliotropic 
animals positive through cooling, it was also possible every 
time to make positively heliotropic animals negative through 
heating. Ihave repeated the experiments many times, and 
besides have demonstrated them to others. After what has 
been said I need scarcely mention that positively heliotropic 
animals become more energetically positive through cooling, 
while negatively heliotropic animals become more energetic- 
ally negative through warming. 
3. The heliotropism of Polygordius larvee can also be 
influenced by light. This influence consists chiefly in the 
fact that direct sunlight makes positively heliotropic animals 
negative. I did not succeed in making negatively heliotropic 
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