io6 Studies in Animal Behavior 



relation between the class of chemical used and the 

 influence of the substance on phototaxis. The experi- 

 ments of Jackson on the fresh water amphipodHyal- 

 lella, which is normally negative, have shown that 

 positive phototaxis may be produced by several acids, 

 ammonium hydroxide, and several other chemicals. 

 Michener found in experimenting with a number of 

 diverse forms that if the response is negative it 

 may be rendered positive by chemicals, although 

 positive forms are rarely made negative. Acids, 

 alkalies, salts and various other chemicals of the 

 most diverse sorts would often change the photo- 

 taxis from negative to positive. There was a marked 

 similarity of effect produced by chemicals of the most 

 diverse kinds. 



While reactions to light may be reversed by many 

 agencies, light in turn may reverse reactions to other 

 stimuli. During the last few years there have ap- 

 peared several interesting studies on the influence 

 of light and other agencies on responses to gravity. 

 Esterly, in studying the reactions of the copepod 

 Calanus, found that individuals when in the dark be- 

 came negatively geotactic, but when illuminated 

 either from above or from below they swam down- 

 ward. Similar behavior was observed by Harper 

 in the larva of the fly Corethra, by Bauer in the 

 crustacean Macromysis, and by McGinnis in the 

 fairy shrimp Branchipus. The recent work of Dr. 

 Dice on the vertical migrations of Daphnia has 

 shown that the changes in the vertical migrations of 



