250 'Journal of Comparative Neurology and Psychology. 



the directive influence of light of sufficient strength. In these 

 cases, it was observed that the photopathic reaction was invariably 

 subservient to the phototactic, although the latter was also very 

 dependent upon a certain optimal intensity for bringing about a 

 positive or negative response. In the following instance we shall 

 observe that, although the directive influence of the light rays is 

 capable of modifying the orientations which relative intensities of 

 light have determined, still the directive influence can not quite 

 obliterate the evidence of a photopathic reaction, as was possible 

 in the younger larvae. In other words the tendency of the fifth- 

 stage lobster to "select" the darker regions has become almost as 

 firmly fixed as has the tendency to react negatively to the directive 

 influence of the light rays. In the first larval stages the photo- 

 pathic response invariably gives way to the phototactic. In the 

 fifth the two tendencies clash; and the resulting orientation of the 

 lobster is determined, not by one, but by both of these factors. 



{A.) Case J. Photopathy versus phototaxis — Ten fifth-stage 

 lobsters were put in box B. This was mounted upon the colored 

 glass plates over the light-shaft as in previous experiments. The 

 preliminary observation showed that there was a definite tendency 

 for the lobsters to congregate at the red end of the series of glass 

 plates, thus demonstrating a negative photopathic reaction. Now 

 the window at the red end was opened to difi^use light. After a 

 period of ten minutes, observations of the position of the lobsters 

 were begun, and continued at five-minute intervals. The follow- 

 ing results show that, although the negative phototactic response 

 is still manifested, it has been greatly modified by the tendency on 

 the part of the lobsters to avoid the brightly illumined area at the 

 end of the box: 



Daylight. Green. Orange. Red. 



1423 



» 3 3 3 



2332, 



3 4 



2 4 



3 i 



19 15 



In the next case, the end of the glass plate series, which in the 

 previous instance admitted reflected daylight, was covered with 

 a blue glass and the illumination of this area thus rendered less 



