THE CONTROL OF PHOTOTACTIC REACTIONS IN 

 HYALELLA BY CHEMICALS 



HARTLEY H. T. JACKSON 



From the Zoological Laboratory, University of Wisconsin 



Loeb 1 in a brief preliminary paper has shown that specimens 

 of Gammarus pulex, which are normally negatively phototactic, 

 may be made positive if they are placed in certain chemicals of 

 the proper degree of concentration. For example, positive photo- 

 taxis was produced when the amphipods were placed in solutions 

 of hydrochloric, oxalic or acetic acid of about m/500. Loeb 

 obtained similar results with a 2^m solution of ethyl alcohol, a 

 m/6 solution of ether, and a m/25 solution of ammonium chloride, 

 but a m/10 solution of boracic acid failed to produce such an 

 effect. My own experiments were performed on another amphi- 

 pod, Hyalella knickerbockeri, in the endeavor to ascertain if 

 Loeb's results would hold true in this species, and to test the 

 effect of various chemicals in different concentrations. The results 

 obtained were similar to those of Loeb, but it was found thatHya- 

 lellas were made positive by boracic acid if they were dropped 

 into a saturated solution. Tartaric acid produces no change in 

 their reaction. 



My results with salts were quite parallel to those of Loeb; I 

 found some ammonium salts to make them decidedly positively 

 phototactic; some potassium salts made them weakly positive; 

 potassium bromide and potassium iodide made them strongly 

 positive. Potassium chloride and potassium chlorate produced no 

 marked change in their phototactic response, nor did any of the 

 sodium salts, or magnesium sulphate. I tried several alkalies, 

 but here, as with the salts, there seemed to be no relation be- 



^oeb, J. The Control of Heliotropic Reactions in Fresh-water Crustacean, 

 by Chemicals, especially CO>. University of California Publications. Physiology 

 vol. 2, p. 1. 1904. 



