238 VASIL OBRESHKOVE 



of equal intensity were placed one on each side of a rectangular 

 aquarium containing the larvae of barnacles, collected in a 

 blackened pipette, the animals when freed oriented themselves in 

 their swimming in such a manner as to form a trail at an angle of 

 90° to a line connecting the two lights. When the lights were of 

 unequal intensity, the trail formed was toward the weaker light. 

 The degree of deflection was found to be dependent upon the 

 ratio of the two intensities used, thus showing in a relative way 

 that the effect produced is dependent on the amount of energy 

 received. 



Loeb and Wasteneys ( '17) experimented with Eudendrium, and 

 the results were similar to those obtained by Blaauw. 



In some recent publications Hecht ('18, '19a, b, '20) has 

 recorded a series of readings representing the photic sensitivity 

 of Ciona intestinalis and Mya when the tmie of exposure and the 

 intensities of light were varied. The results obtained leave no 

 doubt that the velocity of change in the receptors during illumi- 

 nation is dependent upon the intensity and the time of action. 

 He has pointed out that to produce in an animal, a reflex due to 

 light the tune required is inversely proportional to the intensity 

 of the light and therefore that the product of these two is a con- 

 stant quantity for all conditions. 



III. MATERIAL AND METHODS 



Tadpoles of Rana clamitans are very abundant in the ponds in 

 the vicinity of Cambridge and Boston. The tadpoles transform 

 the next season after hatching, thus covering two breeding 

 seasons. Hence during any month of the year there may be 

 found in the ponds tadpoles of various sizes; some that were 

 hatched during the preceding spring and others that are about 

 to transform. 



Animal dealers in Boston keep the tadpoles of Rana clami- 

 tans for sale throughout the year, and from these sources the 

 greater part of the material for the expermiental work was 

 secured. On several occasions, however, the animals were 

 brought directly from the ponds into the laboratory. Such 

 tadpoles usually were found much overfed and inactive and 



