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 
ina few minutes at a constant temperature of about 15° C., had 
no effect upon the same animals when the temperature was 3— 
7°C. 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°C. 
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 concentratiou 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 larvee 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: 0.6g., 1 g., 1.3 g., and 
1.6g. 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 larvee 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- 
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