VARIATIONS IN REACTION TO LIGHT. 11 
Drscriprion OF HXPERIMENTS 
Eeperiment [.—A tow-netting was taken in Port Erin Bay, April 
cist, 12—1 pm. After stirring up in sea-water, it was divided into 
ve portions of 300 ¢.c. each, which were placed in white soup plates and 
reated as follows :— 
No. 1.—Control, untreated. 
+ > 
Jk 
iN 
No. 2.—Added 3 c.c. of 79 HCl, making 1000 Solution. 
+ 
Nive ested N 
No. 3.—Added 6 c.c. of 7 HCl, making zp solution. 
0 500 
No. 4.—<Added 3 c.c. of 7g NaOH, making j6¢@ solution. 
> 
| 
N N 
No. 0.—Added 6 c.c. of j7 NaOH, making 509 solution. 
The dishes were left in the diffuse daylight of a north window, and 
examined after two hours (3 p.m.), the arrangement of the organisms is 
found to be the same in all five plates, showing no change due to acid or 
alkali, and this persisted throughout the experiment. 
In each of the dishes there are two prominent groups of organisms, 
a larger group at the part nearest the window and close to the surface of 
the water, a smaller, but well-marked group at the diametrical pole 
farthest from the window and at the bottom of the plate. 
On shading, for a few minutes, half of one dish with a cardboard, 
the line of shade of edge of cardboard being at right angles to the plane of 
the window, in the illuminated half of the plate there is a thick group at 
the nearést point to the window; in the darkened semicircle, immediately 
on hfting the card, a smaller group is seen at the point distal to the ight, 
and also there is a diffusely scattered but increased number over all this 
previously dark half, much greater than in corresponding areas of the 
illuminated half. 
1, Quoted by Holt & Lee, loc cit. 
