266 



VASIL OBRESHKOVE 



is, therefore, gradual and it seems to proceed with an approxi- 

 mate constancy. 



The photodynamic nature of Rana clamitans tadpoles, there- 

 fore, differs from that of Ciona (Hecht, '18) and of Mya (Hecht, 

 '19 a, b, '20) in that nearly all of the reaction-time in the tad- 



Zj 0J2 



E 



§0^9 



O 006 



1- 



a. 



C^ 



^nlensity- Covdie meters. 



Fig. 7 Curve A represents the relation of the reciprocals of reaction-times 

 of tadpoles with eye and skin, minus a probable secondary period of 0.7 second, 

 plotted on the ordinates, as function of intensity, plotted on the abscissa. Curve 

 B, reciprocals of reaction-times of blind tadpoles, minus 0.7 second, plotted on 

 the ordinates as function of intensity of light. 



poles represents a sensitization period and that the time occupied 

 for secondary processes seems to be extremely short. 



In view of the close agreement between the intensity-reaction- 

 time products up to 20 candle-meters and the consistency of 

 deviation with the higher illuminations, it appears that the 

 Bunsen-Roscoe law holds true only within a certain limited 



