SPECTRAL COLOR AND STIMULATION 515 



raised and lowered. Sometimes they were found to be negative 

 and sometimes positive, but during all of this time orientation 

 was rather indefinite excepting for short periods until in the 

 afternoon of the third day, when the colonies were found to be 

 very strongly positive and orientation was fairly precise. The 

 only extensive series of tests obtained with Spondylomorum was 

 made at this time. The results of this series are given in table 

 11, columns 2, 3 and 4. 



A comparison of these results with those obtained with Pah- 

 dorina and with Eudorina (table 15) shows that the relation be- 

 tween stimulation and wave-length is essentially the same for 

 all. Moreover the results obtained in short series of tests made 

 with negative colonies indicate that the response is the same as it 

 is in positive colonies, just as it was found to be in Pandorina and 

 a number of other forms. 



Arenicola cristata 



The larvae of Arenicola used in the following observations 

 were obtained from eggs, expressed from Woods Hole, Mass., to 

 Cleveland. The eggs were shipped September 16 and received 

 September 18. The following day there was a considerable num- 

 ber of larvae apparently in excellent condition. They were 

 strongly positive and oriented accurately but they deflected 

 somewhat to the right. This accounts for the low results ob- 

 tained as compared with those obtained in observations on Eu- 

 glena under the same conditions. 



Several series of tests were made during the day. In the first 

 four the spectrometer slits were 0.75 mm. wide and in the last 

 two 2.5 mm. wide. All of the results obtained in these tests are 

 given in table 12. The next, day the larvae were again tested 

 but they were found to be too sluggish and their responses too 

 indefinite for successful work. 



By referring to table 12 it will be seen that the four series 

 of results obtained in the first set of tests are nearly alike, and 

 that the regions of maximum stimulating effect and maximum 

 stimulating efficiency lie respectively in the blue between wave- 

 lengths 483 and 493 mx, very near wave-length 483 nn. It will 



