280 STUDIES IN GENERAL PHYSIOLOGY 
lution the animals at first showed no reaction; they fell to 
the bottom, and remained there as though dead. Later a 
few recovered, which, without exception, were positively 
heliotropic. 
Animals which were already positively heliotropic in 
normal sea-water became more energetically so when intro- 
duced into concentrated sea-water. 
Dilute sea-water made the larve negatively heliotropic. 
To three dishes, each containing 100 c.c. of sea-water, were 
added 20, 40, and 60 c.c., respectively, of fresh water. All 
the solutions were at room temperature. Positively helio- 
tropic larvee were distributed in sufficient numbers into these 
three solutions. 
The larve remained positive in the first solution of 100 
c.c. of sea-water + 20 c.c. of fresh water. Only three of the 
thousands of larve which I had introduced into this solu- 
tion became negatively heliotropic. In the second solution 
only about half of the animals remained positive, the other 
half at once becoming negatively heliotropic. In the third 
solution of 100 c.c. of sea-water + 60 c.c. of fresh water the 
animals lay on the bottom for a few minutes without react- 
ing, and then they slowly recovered, and all crept to the 
room side of the vessel. Without exception they all be- 
came negatively heliotropic. Negatively heliotropic animals 
when introduced into the diluted sea-water become only 
more strongly negative. 
We must ask the question whether the suddenness of the 
change in the concentration of the salt solution, or merely 
the absolute concentration, determines the change in the heli- 
otropism. In answer it must be said that on the same day, 
and generally also on the next day, there is no change in the 
behavior of the animals when they remain in the same solu- 
tions. But after that changes may occur. It must be kept 
in mind that the amount of water contained in the tissues of 
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