SELIG HECHT 



163 



All the experiments made to test this prediction verified it with 

 amazing unanimity . Cionas which had been in the dark for several 

 hours were exposed to a light of 2,000 candle meters at regular inter- 

 vals of 1 minute and the reaction time at each exposure noted. The 

 Jesuits of four experiments are given in Figs. 4 and 5. 



The upper curve in Fig. 4 represents the actual data, the moments of 

 'Stimulation being the ordinates and the sensitization periods the ab- 

 scissae (upper scale) . The curve has the usual Weber-Fechner appear- 

 ance, its logarithmic nature being shown in the lower curve of the 



/o 



<3ens / f/2af/on Fer/od — 

 zo JO 4-0 



Seconds 

 so 



60 



I.OG. o/ Sens iff zaf ion -Fer/od 



Fig. 4. Upper curve gives sensitization periods of a Ciona during regularly 

 repeated stimulation at minute intervals. Its logarithmic nature is shown by 

 the lower curve which gives the logarithms of the same sensitization periods. 



same figure. The lower curve has the same ordinates, but the ab- 

 scissae are the logarithms of the sensitization periods (lower scale). 

 That the points form a straight line is undoubted. 



In Fig. 5 are given the data for three other animals. The logarithms 

 of the sensitization periods are plotted as before, and in each case the 

 points very clearly form a straight line. 



This series of experiments therefore is entirely consistent with the 

 three cardinal features of the hypothetical chemical system proposed 

 as an explanation for the photic sensitivity of Ciona. These are, first, 



