LIGHT REACTIONS OF TERRESTRIAL AMPHIPODS 345 



going towards it in a straight path. I placed the light at dif- 

 ferent points of the plate, usually directly opposite the entrance, 

 or on the right and left sides. The specimens would turn very 

 definitely to the side on which the light was placed. 



The formation of habits of turning was very marked. If, 

 after the animal had traveled three or four times to the right 

 side, the light was transferred to the left side ; the animal, 

 when placed again at the entrance, would go to the right. This 

 happened usually once, as in succeeding trials it would turn to 

 the light. 



The behavior of 0. traskiana between glass plates is of interest 

 not only on account of its bearing on the importance of contact 

 stimulation, but also in its relation to orientation. That orien- 

 tation here is not a forced one, but is to a great degree under 

 the control of the animal, seems clearly brought out in several 

 ways. 



The normal way that 0. traskiana travels to the light is by 

 running on its legs. When lying on its side under a glass plate, 

 it gets to the light by pushing itself with legs and body. It 

 will curve its body backward and forward without hesitation 

 to keep the light in its eyes. 



Besides pushing itself to the light, Orchestia will jump directly 

 toward it, when the light is held above the dish. Jumping does 

 not occur when the dish is illuminated from beneath. When the 

 light is held level with the dish, excited specimens will run part 

 of the way toward the light, and jump the rest of the distance. 

 Usually when they jump, they turn over in the air, and land 

 with the head away from the light. They immediately, in fact, 

 so quickly that it is hardly noticeable, turn to the light and 

 jump again. 



0. traskiana, therefore, has a choice of three methods of 

 reaching the light: running, pushing and jumping. Can we 

 suppose then, that the creature is wholly forced by the equal 

 or unequal stimulation of the light on its musculature to take 

 a position with reference to the stimulus, and travel toward 

 or away from it? To v some degree it is. This is shown by the 

 circus movements that occur when the stimulus is shut off 

 from a sensitive. atea. The control of these circus movements 

 in the Orchestia and in other forms, shows the beginning of 

 the control of orientation found in the higher animals. The 



