TRANSFORMATION OF HELIOTROPIC ANIMALS 279 



at a temperature of 15 C., the majority of the animals were 

 negatively heliotropic. The sunlight, which had before and 

 later made the majority of the animals negatively heliotropic 

 in a few minutes at a constant temperature of about 15 C., had 

 no effect upon the same animals when the temperature was 3- 

 7 O. When I returned the animals to the north room, they 

 all again became positively heliotropic, even though the tem- 

 perature at the same time rose to 21 0. 



I have repeated these experiments many times, with 

 numerous modifications, but always with essentially the same 

 result. 



4. Further experiments showed that through an increase 

 in the concentration of the sea-water the same results can 

 be obtained as through a lowering of the temperature. Neg- 

 atively heliotropic larvce become positively heliotropic, 

 and positively heliotropic larvce become still more positive. 

 Through a decrease in the concentration of the sea-water 

 the same effect is obtained as through an increase in its 

 temperature. The positively heliotropic animals become 

 negatively heliotropic, and the negatively heliotropic animals 

 more strongly negative. 



I prepared four solutions of a higher concentration than 

 the sea-water by adding chemically pure sodium chloride to 

 the normal sea- water. To each 100 c.c. of sea-water the fol- 

 lowing amounts of salt were added: 0.6 g., 1 g., 1.3 g., and 

 1.6 g. In order to avoid differences in temperature I allowed 

 the solutions, carefully protected from evaporation, to stand 

 for a day in the room in which the animals were kept. 

 Polygordius larvje which were energetically negatively helio- 

 tropic were then distributed into these solutions. The 

 majority remained negatively heliotropic in the weakest 

 solution, but a few of the animals went to the window side. 

 In the next three solutions almost all the animals at once 

 became positively heliotropic. In the most concentrated so- 



