VARIATIONS IN REACTION TO LIGHT. 18 
once there was a change; three of the five, viz., Nos. 3, 4, and 5, were now 
altered to positive, while Nos. 1 and 2 were mixed, partially positive and 
partially negative. , 
The plates were left in the dark room over-night, the only trace of 
illumination being a very faint ruby light, coming from a small borrowed 
hght through the double thickness of a ruby window and ruby photo- 
eraphic screen. 
The following morning, as soon as a light was struck in the dark- 
room, it was seen that all the organisms in all the plates were collected 
at the points nearest to the faint ruby light. 
The small oil lamp was lit and the plates arranged round it; all five 
showed the organisms strongly postive, Taken out immediately from the 
lamplight to the diffuse daylight of the north window again, the organisms 
in all five are found to be strongly negative. No interval save the time 
of shifting the plates out from dark room to window bench elapsed 
between these two observations with reversed results, 
Experiment I[.—Tow-netting taken by Professor Herdman, on April 
20rd outside the Bay. On standing in diffuse daylight of north window, 
two large groups separate in the glass jar; as usual, one towards light 
and at top, the other away from light and at bottom of jar. These two 
groups were separated off by pipetting into two soup plates, one containing 
the positive group, the other the negative group, and both were found to 
consist chiefly of Naupliu of Balanus. 
The negative group was taken first for examination in the dark room. 
On lighting one candle the organisms swim to the opposite pole; on 
placing two candles at opposite diameters of the plate, the organisms lie 
in the middle, half-way between the two hghts; with four candles placed 
around equi-distant, the organisms are clustered compactly at the centre 
of the plate. The positive organisms similarly examined show a grouping 
around the periphery of the plate accentuated opposite each candle. 
The organisms were left in the dark room overnight and examined 
in it next morning. On first striking a light, both sets of organisms were 
seen clustered at nearest point of each plate to the exceedingly faint ruby 
light. One candle was lit and placed close to the plate containing the 
