The Effect of Exposure Period and Temperature on the Photosensory Process in Ciona

Mya and Ciona are two animals which are sensitive to light, and which respond to it by a vigorous retraction of the siphons. As a result of previous work~ it is known that the receptor mechanism underlying this sensitivity to light is composed of two associated processes. The first of these takes place during the necessary exposure to light. I t follows the Bunsen-Roscoe law, and is practically uninfluenced by temperature. This primary process is therefore photochemical in nature. The characteristic siphon response of the animals does ,not take place immediately after the necessary exposure to light, but only after a definite latent period. The second peripheral process occurs during this latent period, and occupies practically all of it. Only an insignificant portion of it is concerned with the conduction of the stimulus. This secondary, latent period process in Mya has a temperature characteristic of ~, = 19,680, and is uninfluenced by light. I t is therefore probably an ordinary "dark" chemical reaction. The relation between the initial photochemical reaction and the secondary latent period reaction is such for Mya that the velocity of the latent period process is directly proportional to the concentration of the products resulting from the photochemical reaction. From