386 



CHRISTINE ESSENBERG 



One hundred candle power 



29 

 30 

 29 

 27 

 34 

 30 

 29 

 24 

 31 

 30 

 25 

 21 

 25 

 23 

 23 

 26 

 28 

 31 

 • 20 



Thirty-two candle power 



5 



4 



5 



7 







4 



5 

 10 



3 







9 

 13 



9 

 11 

 11 



8 



6 



3 

 14 



If Notonectas are put in a high jar and light admitted from 

 below, the bugs are more numerous at the bottom. If the 

 light shines from above, the bugs are more numerous on the 

 surface. This proves that Notonectas have a strong positive 

 phototaxis. However, their phototaxis may be modified by 

 some such factors as temperature. Thus, an increase in tem- 

 perature results in an increase in phototaxis, as shown in table 

 following : 



Number of Notonectas, thirty-four. Two lights, one sixteen 

 candle power, the other one hundred candle power, were placed 

 at either end of the aquarium and were turned on alternately 

 every five minutes and the animals counted. The number 

 moving toward the light is indicated by a plus sign, those moving 

 away or at random, by a minus sign. Temperature increased 

 gradually. 



Weak light Temperature Strong light 



