2l6 



C. F. PHIPPS. 



III. Responses of Treated Amphipods to Light Intensity 

 AND TO Direction of Rays. 



(A) Potassium Cyanide. — Only stock kept in the laboratory 

 for some weeks was used in these experiments. Three different 

 strengths of cyanide were tried, N/ioo,ooo, N/125,000, and 

 N/150,000. Both reversed and normal responses occurred with 

 all three. Probably the N/ioo,ooo is not too strong for work 

 with these animals and quicker results may be obtained with 

 this strength. The animals were kept in the different solutions 

 for varying lengths of time, one to nine days. 



In Table III. the reactions of the three species are shown with 

 the tank in position 2. In this case the Hyalella gave no majority 

 of reversals in any series of readings, though the other two 

 species showed strong reversals. Where the animals were ex- 

 posed a longer time, as with Eucrangonyx, all the experiments 

 gave a majority of reversed reactions. When the tank was in 

 position I or 3 the results were very similar to those in position 2. 



Table III. 



Amphipods Treated with Potassium Cyanide. 



Experimental Tank at an Angle of 45° to Direction of Rays with the Dark End Nearer 



the Lamp {Position 2). 



(B) Chloretone. — For these experiments a solution of 0.0025 

 per cent, was used, which was strong enough to give a very 

 perceptible odor of chloretone. The animals were kept in this 

 solution from 8 to 12 days before experimenting. This length 

 of time exposed undoubtedly was a factor in causing many 

 more reversed reactions than with other treatments. 



When the tank was in position i the Gammarus showed a 

 much larger per cent, of reversed than normal reactions, but 

 the other two species were all normal in the majority of readings. 

 In the other two positions of the tank all three species had strong 



