156 SUMMARY OF CURRENT RESEARCHES RELATING TO 



on the basis of one chemical action of light upon the cell (a katabolic 

 one). The positive state indicates that the speed of reactions in the 

 cell lies below a certain value, which may be called the optimal value, 

 and the negative state corresponds to a speed of reactions in the cell 

 above the optimal value. In the former case the sentient surfaces are 

 turned into the light to increase velocity of reaction up towards the 

 optimal value ; in the latter case the sentient surfaces are turned away 

 from the light so as to decrease the velocity of the reactions down 

 towards the optimal value. 



As a result of the orientation so caused, there arises movement of 

 the organism towards or away from the source of light, but such orienta- 

 tion is not a fixed orientation, but rather a steering action ; the animals, 

 as a result, do not remain in one fixed plane, or direction of movement, 

 but the net result of the movement is that the organisms move to or 

 from the light. In the case of young plaice, the animals may be in all 

 possible planes of orientation to the light when the movement is finished. 



In the nauplii of Balanus movement towards or away from the light 

 has an associated movement upwards or downwards. These two move- 

 ments would coincide in natural conditions. Addition of small amounts 

 of acid or alkali was not found to alter the reactions to light. The rate 

 of movement is almost the same with different intensities of light and 

 different coloured lights, showing that the locomotor apparatus is not 

 affected by the light, but continues to work at the same rate. The 

 nauplii moved from red light to blue light, and from blue to green. 

 Movement in converging and diverging light is described, and shown to 

 be explicable on the basis of intensity of light alone. Direction pro- 

 duces its effects in a secondary manner on account of the light and shade 

 effects of the animal's own body. 



Phosphorescent Copepods were found to be indifferent in regard to 

 movement to light from without. That light from without has another 

 type of influence upon these phosphorescent organisms is shown, how- 

 ever, by the fact that their periods of activity and rest in regard to 

 phosphorescence follow respectively the hours of daylight and darkness. 

 This alternating diurnal periodicity may persist for twelve days in the 

 absence of the accustomed recurring stimulus of day and night. The 

 phosphorescence is spontaneous. When freshly taken the organisms 

 show a faint persisting light, with flashes at intervals. At a later period 

 the light disappears entirely between the flashes, which have a longer 

 interval between them. Under probably pathological conditions, after 

 the organisms have been confined for a considerable period, there may 

 be lighting up of the organisms with a continuous glow. 



The appearance of the spontaneous phosphorescence at nightfall and 

 its disappearance at dawn are characterised by the same changes in a 

 reversed order in the two cases. Before the appearance of spontaneous 

 phosphorescence at night, and after its disappearance in the morning, 

 there is a period of minimal excitability of about half-an-hour, during 

 which stirring still calls out phosphorescence. After this the organisms 

 became completely refractory. 



Additions of fresh water, or formol, produce, during the period in 

 which the organism is dying, a most vivid phosphorescence, which lasts 



