REACTIONS OF LAND ISOPODS TO LIGHT 



213 



The method of calculation is as follows: Each response is 

 given the number of the sector in which it falls as in the second 

 method (fig. 2). For example, in the records of class A in figure 

 4, four of the responses fall into sector 5 and one into sector 6. 

 The average of the five responses is thus 5.2. The middle points 

 of the eight sectors, expressed in terms of angular deviation 

 from the central axis mn are: 1. 11.25°; 2. 33.75°; 3. 56.25°; 

 4. 78.75°; 5. 101.25°; 6. 123.75°; 7. 146.25°; 8. 168.75°. The 

 difference between each of these figures and the succeeding one 

 is 22.50°, or one-sixteenth of 360°. The figure 5.2 expressed in 

 angles is equivalent to the angle just given for 5, 101.25°, plus 

 two-tenths of 22.50°, making 105.75°, the angle of negativeness 

 for the responses recorded in figure 4, A, when the animal was 

 facing the light. 



As an application of this method, table 4 expresses the angle 

 of negativeness for the reactions which were shown graphically 

 in figures 6 and 7. 



The table shows that both of these animals were negative, be- 

 cause they turned, on the average, at least 90° away from the 

 light w^hen they were facing the light, and, respectively, 14° 

 and 32° away when they were already at right angles to the 

 fight. 



The fact that Oniscus A 12 was positive or indifferent on the 

 first day and gradually became negative is shown by the angles, 

 when the animal was stimulated on the side, for the first seven 

 days of the experiment: 1st day, 78.75°; 2nd, 96,75°; 3rd, 

 103.50°; 4th, 85.50°; 5th, 108.00°; 6th, 139.50°; 7th, 139.50°. 



TABLE 4 



Angle of negativeness for Oniscus A 10 {tested for 17 days) and A 12 {tested for 15 

 days). Intensity of light 12.955 CM. Tests were made with the animals facing 

 the light {A), facing away from the light {B), and illuminated on the right (C) and 

 left {D) sides 



