206 CHARLES HARLAN ABBOTT 



An examination of a large number of records showed that 

 Oniscus is decidedly negative to light. This conclusion is shown 

 best, however, by applying to the records more than one method 

 of analysis, in order to give a clearer idea of what'is involved in 

 the negative reaction. Three methods will be described on the 

 basis of results obtained while studying the individual behavior 

 of these isopods on successive days. The three animals which 

 will be particularly considered are designated as A 10, A 11, 

 and A 12. They were placed in all cases in the center of the 

 field, as in the typical method described, and exposed to an 

 average intensity of 12.955 candle meters. 



In making each record, the sex of the animal was recorded. 

 However, no differences were found between the reactions of the 

 two sexes, so that the results of both were used indiscriminately 

 in compiling tables and angles. 



1. Positive and negative response — first method of analysis 



This method of tabulating results is shown in table 1, which 

 summarizes the results from Oniscus A 10, extending over 

 seventeen days. 



Responses are classified as positive or negative according to 

 the grouping explained in figure 3. When the animal crossed 

 the circle within the positive quadrant, the response was recorded 

 as positive; otherwise, it was considered negative, because the 

 animal went into a region of diminished intensity. The letters 

 A, B, C, D refer to the four positions in which the animal was 

 placed with reference to the light. 



The results are given in percentages of each kind of response. 

 The positive responses number 5.9 per cent, and the negative 

 responses, 94.1 per cent. The variation in the four columns 

 A, B, C, and D is slight, showing that the-direction in which the 

 isopod was headed made little difference in the nature of the 

 response. This Oniscus was thoroughly negative to light, 

 although in a few isolated instances it went toward the light. 

 If the positive response were 25 per cent of the total, it might be 

 concluded that the animal was indifferent to light, as the posi- 



