666 LATENT PERIOD OF MYA 



as the investigation of the photic sensitivity of Mya and other ani- 

 mals proceeds. The concreteness of the conception, however, should 

 prove a useful tool in the acquisition of additional knowledge in this 

 field. 



SUMMARY. 



The latent period in the response of Mya to illumination varies 

 inversely as the duration of the exposure to which it is subjected. 

 The reciprocal of the latent period, measuring the velocity of the 

 process which underlies it, is a linear function of the exposure period. 

 Since the duration of the exposure represents the amount of photo- 

 chemical activity, it is concluded that the substances formed at that 

 time act to catalyze a chemical reaction which determines the dura- 

 tion of the latent period. 



This explanation is in accord with the previous work on the photo- 

 chemical reaction and with the effect of temperature on the latent 

 period. As a result of the combined investigations there is presented 

 a concrete hypothesis for the mechanism of photic reception in Mya. 



BIBLIOGRAPHY. 



Arrhenius, S., Quantitative laws in biological chemistry, London, 1915. 



Euler, H., General chemistry of the enz5mies, New York, 1912. 



Hecht, S., {a) Sensory equilibrium and dark adaptation in Mya arenaria, J. Gen. 

 Physiol., 1918-19, i, 545; {b) An analysis of the relation between the tem- 

 perature and the duration of a biological process, Proc. Nat. Acad. Sc, 1919 

 V, 146. 



Sheppard, S. E., Photochemistry, New York, 1914. 



Weigert, F., Die chemischen Wirkungen des Lichts, Stuttgart, 1911. 



