96 A. M. REESE. 



REACTIONS OF NECTURUS TO LIGHT. 



The same kinds of experiments were tried with Xccfitnts as 

 with Cryptobranchus. All parts of the body seemed sensitive to 

 white light, but in this case the head was more sensitive than 

 the tail, the withdrawal from the circle of illumination being in- 

 stantaneous, in many cases. 



The effect of illumination from below was also tried with Ncc- 

 ti/n/s, the animals being placed in a glass aquarium which was 

 shaded from above, while a beam of sunlight was thrown on the 

 ventral regions of the body. All parts of the ventral surface 

 were sensitive to this form of stimulation, but the head was, in 

 this case, much less sensitive than the tail. The responses as a 

 whole were neither so quick nor so strong as when the light fell 

 upon the dorsal regions of the body. 



A beam of red light produced by the same red plate that was 

 used in the experiments upon Cryptobranchus produced no reac- 

 tions that were definite enough to be of value. The red, incan- 

 descent bulb, on the other hand, caused fairly strong reactions, 

 those from the head and tail being of about the same sudden- 

 ness. 



The reactions to blue light, whether produced by the plate or 

 the incandescent bulb, were much more decided than those to red 

 light; the average reaction time for the head and for the tail was 

 about the same. 



No experiments were tried to determine the effect of red or 

 blue light upon the ventral side of the body, either with Crypto- 

 hrauclins or with Ncctiints. 



That it is not the organs of the lateral line system that respond 

 to these light stimuli seems probable, at least in Cryptobranchus, 

 from the fact that the head region, which is most abundantly 

 supplied with the organs, is less sensitive to light than is the tail. 

 In Necturus, when the light came from above, the head gave the 

 most sudden responses ; but when the light was from below the 

 tail was more responsive than the head. This would seem to 

 indicate that the more rapid response from the head was due to 

 the sensitiveness of the eves, though whv this should be the case 



- o -< 



with Ncctni'iis and not with Cry'pto'irancJius is not apparent. 



