REVERSIBILITY OF HELIOTROPISM OF ARENICOLA LARVJE. l6l 



Table VI., the temperature coefficient (Qi ) of the maximum 

 reversal of the normal heliotropism appeared to be between 2 

 and 3. The reversal may, therefore, be interpreted as the 

 result of a chemical reaction. The marked physiological activity 

 of the fatty acids seems to depend largely on their lipoid-solu- 

 bility. At lowered temperatures their effectiveness in producing 

 negative heliotropism is somewhat lessened, as Table VI. shows. 



TABLE VI. 



EFFECTS OF FATTY ACIDS. 



Of all chemicals tested by the writer, fatty acids were the best 

 for reversing normal heliotropism. If one reversed the helio- 

 tropism of a mass of larvae by fatty acid, a large percentage 

 gradually accumulated at the side of the dish away from the 

 light. If now one turned the dish through 180, it was most 

 striking to see the hosts of larvae quickly assume the new orien- 

 tation and swim to the negative side. Their general behavior 

 and activity appeared normal. Many, however, swam at the 

 bottom of the negative side of the dish, especially in solutions 

 of the higher fatty acids. Curiously enough, this efficiency of 

 fatty acids as a reverser of heliotropism runs closely parallel to 

 their physiological efficiency in producing artificial partheno- 

 genesis, as discovered by Loeb. 



