REACTIONS OF LAND ISOPODS TO LIGHT 



229 



(22.5°) between any two adjoining classes of the eight grades of 

 negativeness (fig. 2). The smallness of this range is shown dia- 

 grammatically in figure 13. 



2. Porcellio showed a much wider variation, the differences 

 between the lowest (61.87°) and the highest (119.25°) aver- 

 ages recorded being 57.38°. This also is shown in figure 13, 



Qniscus 



Fig. 13 Diagrammatic representation of the comparison of the reactions of 

 Oniscus and Porcellio given in table 10. The shaded areas show the range of 

 the average angles of negativeness under the six conditions, when the animals 

 were illuminated on the side (positions C and D). Porcellio has a wider range 

 than Oniscus, part of the averages showing a slight turn toward the light. 



which shows a considerable degree of variability. In what were 

 probably the more normal of the conditions (i.e., when newly 

 collected, from a dark normal habitat, and from a maximum of 

 moisture), the reaction of Porcellio was negative, but, after con- 

 tinued exposure to strong light and when exposed successively 

 to light of different intensities, the reaction tended to be positive. 



