214 'Journal of Comparative Neurology and Psychology. 



orientation of the larvae was indefinite. Suddenly the rays of a 

 powerful acetylene light were thrown upon the jar. Immediately 

 a negative reaction took place and continued for two minutes, 

 when some of the larvae began to return to the light. At the expira- 

 tion of four minutes all the larvae were reacting positively, and this 

 reaction continued for several hours. 



Experiment y — July 22, 9:30 a.m. Forty-four second-stage 

 lobsters, six days old, were placed in the glass jar, in the dark box. 

 Eleven came at once to the room side of the jar. The jar now was 

 moved nearer the small (three by three inch) window. As a result 

 seventeen out of forty-four individuals gathered on the room side, 

 but the definiteness of the positive reaction on the part of the win- 

 dow-side lobsters was lessened by desultory swimming. The jar 

 was next placed on the west table, the room side and top of the 

 jar being shielded by black paper. All the larvae came to the 

 room side of the jar. When replaced in the dark box (in light 

 of much lesser intensity), the reaction again became uniformly 

 positive. 



Experiment 8 — July 23, 9 a.m. Forty second-stage larvae, 

 seven days old, were placed in the glass jar on the east table, and 

 exposed to strong light. All the larvae at once oriented on the 

 room (darker) side of the jar. These lobsters were next placed 

 on the west table where the negative reaction continued through- 

 out the afternoon. From 6 to 8 o'clock in the evening the light 

 faded gradually. At 7:35 the body-orientation was nearly lost, 

 but the orientation on the room side of the jar with diminishing 

 definiteness remained in effect until 7:50, when the light had faded 

 quite away and the lobsters were scattered throughout the jar. 



Experiment g — July 28, 9:30 a.m. Twenty third-stage lob- 

 sters, twelve days old, were placed in the glass jar in the dark box 

 on a white background and submitted to light of slight intensity 

 coming through the small window. All showed a strong positive 

 reaction, and gathered on the window side of the jar. The next 

 day in the afternoon, about fifty third-stage larvae of the same 

 group, now thirteen days old, were placed in the glass jar in the 

 dark box on white background and submitted to light of medium 

 intensity. Nearly all of the larvae oriented on the room side of the 

 jar, thus demonstrating a definite negative reaction. 



Experiment 10. Case i — June 26, 9 a.m. Ten fourth-stage lob- 

 sters, fifteen days old, were placed in the glass jar in the dark box 



