220 'Journal of Comparative Neurology and Psychology. 



Conclusions from Experiments ii and 12: In the results of the 

 foregoing experiments, we have further evidence to support the 

 conclusions drawn from Experiment 3. In Experiment 12 the 

 larvae passed from a region of greater (blue) to one of lesser (the 

 red, or in Case 3, the bladk) light-intensity in moving toward the 

 source of light in the direction of the incident rays. It must be 

 assumed that in Case 3, there was a much greater difference in the 

 intensity of light at the two ends of the box (overlying the blue 

 glass and the black paper respectively) than in Case 2, or in Experi- 

 ment 3. These experiments were performed many times, under 

 several different conditions of light, and with larvae of ages vary- 

 ing from a few hours to two days. The same results were 

 obtained in every case, except that in the older first-stage larvae the 

 reactions were not so definite (more individual variations) and a 

 stronger light was required to bring about the same responses as 

 were manifested by larvae under four hours old. In these cases, as 

 also in Experiment 3, rays of lesser intensity (but in a horizontal 

 planej which struck the larvae in such a way as to cause a body- 

 orientation in which a normal swimming position was still main- 

 tained, w^re more influential in determining a progressive orienta- 

 tion than were the more intense rays which struck both eyes 

 equally, but which came from below, and had a tendency (as will 

 be shown in detail later) to throw the larvae out of their normal 

 swimming position. As the writer has shown elsewhere (1907a), 

 galvanotactic reactions in the young lobsters occurred only when 

 the tail or the back was turned wholly or partly toward the anode. 

 Although at first sight it appears that the causes for this condition 

 of reaction can have nothing in common with the causes which 

 determine a progressive orientation to the directive influence of 

 light rays only when the swimming position is favorable, it may not 

 be inappropriate to suggest that here also the direction of the 

 impact of light with reference to the axis of the body of the larva, 

 may have some influence on the reaction. 



Experiment ij. Case i — Ten larvae, twelve days old, were 

 placed in box J, mounted over the light-shaft. When the glass 

 plates were arranged in the order designated below, the photo- 

 pathic reaction was as follows: 



