TRANSFORMATION or HELIOTROPIC ANIMALS 281 



an animal is dependent, not only upon the concentration of 

 the salt solution in which it lives, but also upon the amount 

 of water which is lost by secretion. It is therefore clear 

 that in time an adaptation of the animal to the altered con- 

 centration of the sea-water may occur. The temperature in 

 all these experiments was usually about 20 C. 



5. I tried to see whether it is possible to make animals 

 positively heliotropic in a diluted salt solution by lowering 

 the temperature. Positively heliotropic larvae were intro- 

 duced into sea-water to which 72 per cent, of fresh water, 

 by volume, had been added. At the beginning of the ex- 

 periment the temperature was 19.5 C. The animals at 

 once became negatively heliotropic. I then began to lower 

 the temperature. At the same time as a control I subjected 

 a number of negatively heliotropic animals contained in 

 normal sea-water to the same lowering of temperature. 

 When the temperature reached 11 C., a few of the animals 

 in normal sea- water became positively heliotropic, and at 

 7 C. the majority of the animals in normal sea-water 

 became positively heliotropic. In the dilute salt solution, 

 on the other hand, all the animals remained negatively 

 heliotropic. Only they reacted more slowly than the ani- 

 mals kept in the normal sea-water. At +4 C. they also 

 remained negatively heliotropic, if they reacted at all ; while 

 those kept in the normal sea-water at this temperature were 

 verv energetically positively heliotropic. When the tem- 

 perature again rose, the reactions of the animals in the dilute 

 sea-water again became lively, but they, of course, remained 

 negatively heliotropic. I have mentioned the fact that ani- 

 mals which have been kept several days in dilute sea-water 

 may again become positively heliotropic. In such animals 

 it was also possible by lowering the temperature to make at 

 least a few positively heliotropic. 



6. It is worthy of note that I found the same dependence 



