132 S. J. HOLMES 



was inserted into the mouth somewhat farther than the level 

 of the nerve ring and a small slit was made in five places. The 

 specimens were placed in running water and showed little effect 

 of the shock of the operation. Some were experimented with 

 soon after the nerve ring was cut ; others were allowed to remain 

 quiet for several days before being disturbed. As a rule the 

 individuals operated on were in good condition and even the 

 organs nearest the cuts showed little change in the character 

 of their responses to local stimulation. Local responses to light 

 and shadows occurred in the same manner as in normal sea 

 urchins, and the general responsiveness of the animals indicated 

 that shock effects played a comparatively small part in caus- 

 ing any changes which may have occurred in their behavior. 



Numerous experiments were tried with the specimens operated 

 on in order to give them every possible opportunity of show- 

 ing a phototactic response. Neither in dim light, nor in direct 

 sunlight was there any well defined movement away from the 

 stimulus. Most of the experiments were carried on by exposing 

 one-half of the animal to direct sunlight while the other half 

 was shaded, as sea urchins have been found to respond most 

 readily to light under these conditions. Continued experimen- 

 tation with numerous individuals, with repeated intervals 

 of rest in the dark to increase their sensitivity failed to elicit 

 any movement away from the light in any sea urchin in which 

 I was sure that the nerve cord had been cut. The lack of loco- 

 motor response was apparently not due to any failure in the 

 response of the organs stimulated. If a sea urchin has one- 

 half of the shell exposed and the other half shaded, the spines 

 on the stimulated areas move more actively, as if they were 

 making ineffectual attempts to carry the animal into the shade. 

 The tube feet on the equatorial and upper regions of the body 

 are more retracted on the stimulated side, while they are fre- 

 quently much extended on the shaded side. The whole animal 

 squirms and twists about uneasily, but it seldom gets more than 

 a few millimeters from its original position even after hours 

 of exposure, and is then as likely to become shifted in one direc- 

 tion as in another. Such a sea urchin gives one the impression 

 of trying to get away from the stimulus, while being held back 

 by the misguided action of some rebellious tube foot which 

 fails to loosen its hold, or the contrary movement of certain 



