REACTION'S OF CRVPTOBRANCHUS AND NECTURL'S. 95 



In about half of the experiments where light was thrown 

 upon the head of Cryptobranchus no response was obtained even 

 at the end of two and a half minutes or longer, and in no case 

 was a response obtained in less than nine seconds : however, 

 sufficient undoubted responses were obtained to justify the state- 

 ment that the head of the animal is sensitive to white light. The 

 response in this case, when it came at all, was invariably shown 

 by the animal's backing away from the light. 



The responses were about as sudden and as strong when the 

 incandescent light was used as when the much stronger illumi- 

 nations were employed ; this may have been due to the fact that 

 when the rays from the sun or the arc light were used the tank 

 was partially illumined by diffused light, while in the other case 

 there was no light except the small circle that came from the 

 shaded incandescent bulb. 



That Cryptobranchus is sensitive to white light of even weak 

 intensity seems proven by the fact that the animals seek the 

 darker parts of their tank in ordinary diffused light. 



The results obtained with the red and blue lights were not so 

 definite as those with the white light, and, as has been pre- 

 viously stated, may have but little value. With the red plate 

 which gave, with the arc light, a strong, pure red illumination, 

 no responses at all were obtained, either from head or tail stim- 

 ulation. The incandescent light with the rub}' globe, while not 

 so strong a light, produced, in most cases, decided responses ; 

 this was possibly clue to the fact that the light was not nearly so 

 pure a red as that given by the plate. The responses were of 

 the same character as with the white light, the difference being 

 one of rapidity. 



In no case was the response to a stimulus instantaneous, as 

 with the white light, but in several instances reaction took place, 

 when the tail was stimulated, within two seconds. As with the 

 white light, the head was much less sensitive than the tail. 



The reactions to blue light were of the same character as with 



o 



the other forms of illumination, but were more rapid than with 

 the red light. The apparently greater sensitiveness to blue than 

 to red light may have been due simply to the greater purity of 

 the latter color. 



