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 larvae 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 larvaB were distributed in sufficient numbers into these 

 three solutions. 



The larvaB remained positive in the first solution of 100 

 c.c. of sea-water -f 20 c.c. of fresh water. Only three of the 

 thousands of Iarva3 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 -f 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 



