LIGHT REACTIONS OF TERRESTRIAL AMPHIPODS 343 



sponse under the same conditions. Miss Towle found that the 

 negative Cypridopsis would be made positive by simply jarring 

 the vessel in which it was kept with any solid object. When 

 she picked up specimens with the pipette and dropped them 

 into the water, she found the positive response growing stronger 

 with each disturbance. 



Is it the contact stimulus per se, or is it the state of activity 

 or non-activity brought about by contact, that produces these 

 changes in the phototactic response? When an organism is 

 active, metabolic processes are going on within the body, to a 

 greater degree than when the organism is inactive. The ex- 

 periments quoted above, those performed by Holmes on the 

 eastern amphipods, and the experiments on amphipods de- 

 scribed in this paper, have all shown that those conditions 

 which produce a greater activity of the creature, whether external 

 motions of legs and appendages, or internal activity in the form 

 of metabolism, will bring about a positive phototaxis, while 

 those conditions which decrease body activity, such as cold, 

 moisture, quiet and darkness, will cause negative phototaxis. 

 Whatever internal activity might or might not be produced 

 by dipping a Ranatra in water, externally it appeared inactive. 

 "It (a positive specimen) was then immersed in water and 

 laid on the table. Its movements were very sluggish and its 

 responses to light slow. When placed at right angles to the 

 light, it would slowly and stealthily creep away. It did this 

 eight times in succession when the right and left sides were 

 alternately placed toward the light. At the ninth and several 

 subsequent trials, it went towards the light. * * * Then 

 it was picked up and stroked, but it could not be induced to 

 feign death, and as soon as released, it made for the light * 



* *." Here the contact caused by 'picking up and stroking 

 the specimen did not produce negative responses. . 



Further behavior of 0. traskiana under conditions of contact, 

 seems to point rather convincingly to the conclusion that con- 

 tact stimulation per se is not of great importance in bringing 

 about phototactic responses. Positive specimens will travel 

 toward the light lying on their sides, pressed between two glass 

 plates. On first thought, it would seem that contact in itself, 

 would be sufficient to produce a state of rest and a reversal of 

 the phototactic sense, since in its natural state, the creature's 



