270 GERTRUDE MAREAN WHITE. 



EXPERIMENTS. 



For both the shrimp and squid larvae the experiment was 

 performed as follows: A known number of larvae, usually about 

 thirty-five, were inserted into a small glass tube standing upright 

 in the corner of the aquarium where the rays intersected, and 

 allowed to remain one half minute in order to become dark- 

 adapted. Both lights were then turned on simultaneously, and 

 the glass tube carefully lifted out so as to free the larvae without 

 producing currents in the water. The larvae were exposed for 

 one minute, at the end of which interval a partition was slipped 

 down into the aquarium in such a way as to separate the halves 

 facing the two sources of light. The larvae in each half were then 

 counted and the number recorded ; the light which had attracted 

 the more larvae was considered the more effective. In this 

 manner for each filter numerous readings were taken with the 

 movable lamp at various distances from the container, until the 

 point was found at which the larvae were equally distributed with 

 respect to the two lights. At this point the stimulating effect of 

 the light from the two lamps was, as previously stated, equal. 

 The filters were found to differ in their effect in stimulating both 

 the shrimp and squid larvae, that is, for certain filters the movable 

 lamp had to be placed nearer to the aquarium than for others, in 

 order to obtain an equal distribution of the larvae in the two 

 halves of the container. Table II. and Fig. 4 summarize the 

 results obtained. 



RESULTS AND CONCLUSIONS. 



In this table is shown the relative stimulation of the light 

 transmitted by the different filters. Since the stimulating 

 effect of the light transmitted by each filter is equal to the light 

 produced by the movable lamp when this is so placed that the 

 larvae distribute themselves in equal numbers in the two halves 

 of the aquarium facing the two sources of light, the relative 

 stimulation of light transmitted by the different filters can be 

 expressed in terms of the intensity of the light produced by the 

 movable lamp. This is inversely proportional to the square of the 

 distance of the movable lamp from the aquarium. These values 

 are given in Table II. In order to translate these values on to the 

 basis of relative energy, red filter no. 70 was taken as unity with a 



