BEHAVIOR OF AMPHIPODS WITH RESPECT TO LIGHT. 221 



tends to quiet the animals tends to make them negative." He 

 adds also that the Gammarus pulex, which is negative to light, 

 can be made positive by adding to the water a little carbon 

 dioxid, hydrochloric, oxalic or acetic acid, ether, chloroform, 

 paraldehyde, alcohol, esters and all ammonium salts. Boracic 

 acid, according to Loeb, does not reverse these amphipods, but 

 Jackson ('lo), in repeating Loeb's experiments, but using Hyalella 

 knickerbockeri, found that a saturated solution of boracic acid 

 does cause a reversal, the same as the other reagents. Jackson 

 also found that some other acids and some alkalies produce the 

 same effect. These reversals took place, however, only when 

 he dropped the animals inta the solution, for when he put the 

 animals into distilled water and gradually added the chemicals 

 no reversals took place. 



McCurdy ('13) says that "sunlight modifies the normal physio- 

 logical changes taking place in protoplasm, checking some of the 

 processes and probably accelerating the others. A starfish in 

 the light moves to the shade because of disturbance by light of his 

 metabolism." A part of this disturbance was due to there 

 being "less CO2 given off by the starfish when it was put in the 

 sunlight." 



(B) Metabolism, Physiological States and Reactions. — Before 

 answers can be given to many questions that arise, much more 

 work along these lines must be done. Other methods and treat- 

 ments must be used, such as high oxygen content, caffein, acids, 

 alkalies, carbon dioxid content, etc. 



From the data obtained from this series of experiments it is 

 evident that the responses of aquatic amphipods, like those of 

 many other animals experimented upon, are related directly 

 to the physiological state or condition of the animal. Anything 

 which disturbs the rate of metabolism of the animal alters the 

 response to stimuh. Allee ('12) with isopods. Child ('10) with 

 planaria, Wodsedalek ('11) with may-fly nymphs, and other 

 investigators have found this to be true. 



In these experiments on amphipods then, the reversed re- 

 actions are caused by some change in the metabolic processes 

 of the animals. Potassium cyanide depresses the metabolic 

 processes by decreasing oxidation. Oxidation is decreased by 



