REACTIONS OF LAND TSOPODS TO LIGHT 205 



B. NORMAL REACTIONS 



The actual record of the single set of responses shown in figure 

 5 gives an idea of the usual behavior of Oniscus. That this in- 

 dividual was unquestionably negative to light is sho-svn by a 

 comparison of the reactions in the four positions. The only in- 

 stance in which the animal continued in the direction in which 

 it was headed occurred when it was illuminated from behind 

 and movement straight ahead carried it away from the light. 

 In all other cases it turned very decidedly away from the source 

 of illumination. 



Three different conditions may be noted in the activity of the 

 annual when the box was removed, exposing it to the light: 1) 

 the animal had not come to rest, and merely continued in locomo- 

 tion; 2) the animal had come to rest, but started locomotion at 

 once when exposed to the light; 3) the animal had come to rest, 

 and did not start locomotion at once when exposed to the light. 

 On account of this variation in the initial conditions, these ex- 

 periments with directive light do not show whether locomotion 

 was an effect of stimulation by light. The matter is further 

 complicated by the fact that handling the animals may have had 

 an activating effect, an inhibitory effect, or, as is most prob- 

 able, sometimes one and sometimes the other. However, as these 

 experiments were a test only of the directive influence of light 

 when the animal was already in locomotion, the question whether 

 more than one of these factors entered into the cause of the loco- 

 motion need not be considered. For this reason no record was 

 made of the interval before response in most cases. When there 

 was a delay before response, the antennae were often kept 

 moving, particularly just before locomotion was started, al- 

 though few if any of these movements could properl}^ be called 

 'trial movements.' 



Much individual variation was observed. While the direc- 

 tion of locomotion was usually determined by the light, there 

 were many turns and circles, the causes of which were not so 

 easily analyzed. An example is shown in figure 5, D, response 

 no. 8. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 27, NO. 2 



