378 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



200, or 4.5 per cent, —but it is difficult to explain why they are in 

 the direction of the larger light, instead of the reverse. In the first 

 set of 100 trials with both lights the records of particular individuals 



were not kept separate, 



9 R 7 G 5 4 3 



10 1 



3 4 5 6 



8 9 



is 



10 



14 



12 



^ 10 



8 



C 



4 



t> 







30 



32 



28 



24 



B 20 



10 



12 



8 



4 







&4 



60 



56 



52 



48 



44 



40 



^ 30 



32 



28 



24 



20 



16 



12 



8 



4 







I 1 i I 1 i t 1 : i I I I 1 i 1 I 



I I I I 



III' 



and as it was thought 

 that possibly some ab- 

 normal animal had influ- 

 enced the total, the whole 

 series was repeated on 

 another set of five in- 

 dividuals, these matters 

 being kept in mind ; but 

 the results were entirely 

 comparable with those 

 obtained in the first set 

 of experiments. Such be- 

 ing the case, the two sets 

 of records were combined, 

 and are so represented 

 in the table and the 

 diagram. 



The only plausible ex- 

 planation of this unex- 

 pected result which offers 

 itself at the present time 

 is, that at least a portion 

 of the animals were influ- 

 enced by other factors as 

 well as by the light from 

 the two primary sources. 

 Cockroaches, if undis- 

 turbed, are apt to make 

 themselves at home wher- 

 ever they are put, and 

 usually soon settle down 

 to cleaning their antennae 

 or to making an inspec- 

 tion of their surroundings, 

 apparently irrespective of 

 such influences as steady directive light. It has already been men- 

 tioned how the animals came to rest at the end of the runway, 

 waving the antennae about or cleaning them. Similarly, they 



18 



16 



14 



12 



10 



8 



G 



4 



2 







36 



32 



28 



24 



20 



16 



12 



8 



4 







04 



60 



56 



52 



48 



44 



40 



36 



32 



28 



24 



20 



16 



12 



8 



4 







9 8 7 6 5 4 3 



1 1 



4 5 6 



Figure 13. Frequency polygon constructed 

 from results with cockroach shown in Table \1. 

 A, 08 trials to large light alone; B, 200 trials to 

 small light alone ; C, 200 trials to both lights 

 used simultaneously. 



