VARIATIONS IN REACTION TO LIGHT. 19 
peregrinations, they find a suitable stimulus in the feebler ight. But 
when any accident, such as a chance movement stimulated by some other 
cause, sends them again into the beam, they are stimulated to turn away 
from the light, and must again return via the distal glass surface to the 
refuge of the shade again. 
This effect is seen still more strikingly when the red glass strip is 
imterposed on the path of the incident ght; then scarcely a single 
organism is seen on the illuminated strip, but two packed masses are seen 
on each side of it in the shade, and gradually tailing off as the distance 
from the illuminated strip increases. Similar results are seen with 
negative organisms if a narrow opaque white strip, such as a strip of 
cardboard, be lowered into the jar and held in a vertical position at the 
eaustic. When the light is now placed in position, any organisms in the 
course of the beam, or swimming into it from the two dark zones at either 
side of it, turn at once away from the light, and swim along the path of 
the rays towards the caustic and the card; but they do not accumulate to 
any appreciable extent at the card, they swim round its edges and 
accumulate in the narrow feebly-lit space behind it. 
Experiment VI.—With young larvae of the plaice (Pleuronectes 
platessa). 
A number of young plaice larvae, which were five to seven days old, 
were taken from the Fish Hatchery attached to the Station, and placed in 
sea-water in a flat, oblong pie-dish. It was found that they were faintly 
negatively phototactic in diffuse daylight. Contrary to the case of the 
Nauplii, this appeared to be increased in lamplight as well as in direct 
sunlight. When the dish is brought into lamplight in the dark room, it 
is found that most of the larvae after some time are accumulated in the 
half of the dish farthest from the lamp, decreasing to a clear space directly 
under the lamp. There is, however, no such tight packing up as in the 
ease of the Nauplii. 
The interesting point, however, is that there is no evidence whatever 
of orientation in regard to the light; the larvae he at rest with their 
long axes at all possible angles with the line from the lamplight, some 
