LIGHT REACTIONS — ^METABOLISM — ^MAY-FLY NYMPHS 425 



chemical reactions. Causes that accelerate oxidations tend to 

 make animals positive to light and causes that inhibit oxidations 

 produce reactions to shade. Bohn's conclusions are based on 

 his own and Drzewina's ('11) observations. 



Phipps ('15) found that when amphipods, negative to light, 

 are treated with potassium cyanide, chloretone, or were subjected 

 to decreased oxygen tension or to starvation that many of the 

 animals reversed their reactions both to light intensity and to the 

 direction of rays. 



None of these workers measured the effect of the substances 

 upon the metabolism of the animals under investigation. Indeed, 

 this has been done only by MacCurdy ('13), who found that the 

 negative starfish Asterias forbesi gives off less carbon dioxide 

 in sunlight than in shade. He made no effort to control the reac- 

 tion to light. 



Many investigators, beginning with Loeb ('04), have recorded 

 reversals of sign of the phototactic response which could be pro- 

 duced at will; the problem which we set for ourselves was to 

 find whether or not there is any correlation between the sign of 

 the reaction to light and the rate of metabolism of the animal 

 as measured by resistance to potassium cyanide or by carbon 

 dioxide production. For the first part of this inquiry the May- 

 fly nymphs Leptophlebia sp? and Epeorus humeralis (Morgan) 

 were chosen because of their abundance near the laboratory and 

 because Wodsedalek ('11) had found the phototactic reactions 

 of the May-fly nymph Heptagenia interpunctata is readily 

 reversed by chemicals. 



ECOLOGICAL NOTES 



The Leptophlebia and Epeorus nymphs studied lived in moun- 

 tain streams with stony beds and rapid currents such as are quite 

 common in the Berkshire Hills. Their distribution was most 

 carefully studied in Tunnel Brook (near Hoosac Tunnel). In 

 the early autumn when few leaves had fallen the nymphs lived on 

 the under sides of stone and were almost invariably facing up- 

 stream. Their clinging ability enabled them to maintain them- 



