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 larvas 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 : 4o A. M. warm water was poured into the 

 outer vessel. At 10 : 52 the temperature of the dish con- 

 taining the animals \vas 'J5.3 C., and all the animals were 

 still positively heliotropic. Five minutes later, when the 

 l.'inperature 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. I have 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. 



8. The heliotropism of Polygordius larva? 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 



