304 D. H. WEN RICH 



for this individual. When it was responding normally, values 



A 



of a _i -r cou ld be obtained which were comparable. This line 



of experimentation was not pursued very far, but some examples 

 of the results obtained will be given. In one series of experi- 

 ments (Nos. 42-46) conducted on different days, a number of 

 tests were made in the course of each experiment. When the 

 value of light B was allowed to remain constantly at 2 candle- 

 meters, and the value of A varied till the inhibition point was 



A 



reached, the values of A ^ were successively, for the different 



A -j- Jj 



experiments, 0.14, 0.14, 0.10, 0.14, and 0.125, which show a 



fairly close degree of correspondence. In experiments Nos. 44- 



46, further tests were made with higher intensities of light. In 



these additional tests, the value of light A remained constantly 



at 22.2 candle-meters and the value of B was varied till the 



A 



inhibition point was found. In these cases the value of t - ,-, 



A + r> 



at the inhibition point were successively 0.078, 0.08, 0.08, which 

 series also shows close agreement. But the sensitivity in the 

 latter case is seen to be very much greater than in the former. 

 This increase may have been due to an increase in sensitivity 

 accompanying the use of higher intensities of light, as was indi- 

 cated on page 301, or to an increase in sensitivity due to previous 

 stimulation (for the values for the higher intensities were ob- 

 tained after those of the lower intensities) or to both causes. 

 This line of experimentation, if pursued further, would permit 

 the testing out the applicability of the Weber-Fechner law to 

 the behavior of these animals. 



The results obtained from these few experiments on the fresh- 

 water mussel, while incomplete and fragmentary, nevertheless 

 may indicate some lines of experimentation which might profit- 

 ably be pursued further. 



III. RESULTS WITH MARINE SPECIES 



The experiments and results at Woods Hole may be grouped 

 under two heads: (A) qualitative tests with different species, 

 and (B) results with Pecten. 



