REACTIONS OF LAND ISOPODS TO LIGHT 203 



For convenience in manipulating the animals, small cardboard 

 boxes were used, a little longer than the animal and just wide 

 enough to enclose it without allowing it to turn around (fig. 4). 

 When the sowbug had been shoved to the desired position, the 

 box was removed, and the course taken by the animal was 

 observed and recorded. 



In the experiments the isopod was tested successively in four 

 different positions, namely, facing the light (A), facing away 

 from the light (B), with the right side illuminated (C), and with 

 the left side illuminated (D), This was to eliminate errors due 

 to a possible tendency of the isopod to travel in the direction 

 in which it was already headed. 



Fig. 4 Diagram of frame with which animals were manipulated on the 

 table top. 



The reactions were recorded on printed sheets of paper like 

 that shown in figure 5. It contains four diagrams of the experi- 

 mental field, the squares corresponding to the 10-cm. squares on 

 the table. With the aid of the squares it was possible for the 

 observer to duplicate the course of the animal with considerable 

 accuracy. The four diagrams were used for the four positions 

 A, B, C, D just referred to. Each record consisted of twenty 

 trials, five each in the four positions. These were made in the 

 order A, B, C, D, A, B, etc., to avoid effects of immediate repe- 

 tition of the same stimulus. The responses were numbered in 

 the order in which they occurred in the series. Figure 5 is a 

 typical record of the reactions of a normally negative Oniscus. 



