162 



H. U. STEVENS 



The other general factor, besides thigmotropism, which influ- 

 enced orientation was habituation to the reaction box. Inas- 

 much as five different stimuli were used, it is evident that each 

 compared with every other gives 10 combinations. Since each 

 stimulus was presented first upon the one side and then upon 

 the other, the total number of reactions for the five lights was 

 twenty for each crab. The usual order of the reactions is shown 

 in Table I. With an animal which reacted tolerably briskly, 

 a series could be completed in one hour. With most crabs, 

 however, the time was much longer for the reason that the 

 animal seemed to become habituated to the conditions existing 

 in the box. The first few reactions were usually rapid. As the 

 series lengthened, however, the duration of the time spent in 

 the pen increased, until in many instances the work had to be 

 abandoned for that particular day. 



TABLE I 



Shows the Order in which the Colored Lights were Exposed in the Reac- 

 tion Box, the Numbers Indicate the Number of the Experiment in the 

 Series. The Right or Left Position of the Figure in the Column Indi- 

 cates the Right or Left Position of the Color at the Top of the Col- 

 umn. Thus Experiment 6 in the Table Means that Red was Presented 

 on the Right side of the Reaction Box with Blue on the Left. 



i. The color reactions of crabs which have been exposed to white 

 light. — Ten specimens of Oregonia gracilis were used, the sex 

 and number of which are given in the following table. The 

 five lights, with the general arrangements already described, 

 were presented in pairs with an exposure of each color upon 

 the right and left sides. A complete series consisted, for each 

 individual, of 20 reactions, arranged as shown in Table I. This 

 number was secured for every crab except Specimen 9 whose 

 series consists of 18. Although this animal was exposed to 

 the action of the blue and white lights on four successive days, 



