LIGHT REACTIONS OF NEWT 45 



Experiment XXI. — The same animals that failed to respond 

 to the white spot from the microprojection apparatus responded 

 promptly when a beam of sunlight was thrown, by a small 

 mirror, upon various parts of the body. When the light was 

 thrown upon the tail they either started forwards suddenly or 

 drew the tail sharply forward along the side of the body. When 

 the light was thrown upon the head the animal usually backed 

 away from it. Animals in a cloth covered aquarium in a brightly 

 lighted room responded about as promptly as those in the dark 

 room. 



Animals that had been for some time in the dark responded 

 more promptly than those that had been exposed to the light; 

 some of the former fairly jumped when the beam fell upon them. 



Little or no response was obtained when a small beam from 

 a 5 mm. mirror was used instead of a beam that was large enough 

 to illuminate a large area of the animal at one time. 



The animals responded in the same way, and almost as prompt- 

 ly, to a beam of light from below. 



These reactions to a beam of sunlight are quite similar to 

 those described by the author for Necturus (2). 



SUMMARY 



1. Under the conditions of these experiments Diemyctylus is 

 almost always markedly negative in its phototropic reactions to 

 white light, at ordinary temperatures. 



2. At temperatures near 0° C. and 36° C. Diemyctylus is 

 indifferent to white light from above. 



3. The above reactions are the same whether the light fall 

 from above or come from below, though they are usually less 

 marked in the latter case. 



4. Diemyctylus is positively phototactic to lights of all in- 

 tensities, from very weak daylight to an intense arc light. - 



5. At low temperatures this phototactic reaction is inhibited 

 or reversed. 



6. With an intense white light at each end of the aquarium 

 the animals tend towards the less intense light; if neither light 

 be of great intensity, perhaps not reaching a certain optimum, 

 the animals tend towards the more intense light. 



7. Phototactic reaction to pure red light was the same as 

 to white light, possible a little more marked. 



