REACTIONS OF LAND ISOPODS TO LIGHT 



225 



viduals tested were decidedly positive, while the other two were 

 negative. The positive animals were in fact so decidedly posi- 

 tive that two of the three gave positive responses even when 

 they were headed away from the light. The difference is shown 

 in table 9, which summarizes the individual reactions of the 

 five animals after exposure to light, together with a second 

 series of reactions after exposure to dark, made two days later 

 by approximately the same individuals. 



In table 9 the numbers are arranged in order of magnitude, 

 but most of the individuals appear in both columns. • 



TABLE 9 



Individual behavior in the species Porcellio rathkei after exposure to light and to 

 dark. Intensity 12.955 CM. 



These experiments on the influence of preceding illumination, 

 while they were not carried far, indicate the possibility that nega- 

 tive phototaxis in land isopods may be diminished or reversed 

 by exposure to strong light. This appears from the experiments 

 to have been true for some individuals of Porcellio, but the fact 

 that a like result was not obtained from Oniscus makes it less 

 conclusive. 



Jf.. Comparison of reactions of individuals from dry and moist 



habitats 



The moisture conditions of a habitat are not easily measured, 

 but it is possible to place sowbugs in what must be close to the 

 extremes in which they can live, so far as moisture is concerned. 

 For a minimum of moisture, they can be kept in an environment 



