SEEN WITH THE EYE OF A FISH 23 
ticular object on his body, I nailed a row of miniature 
sleepers from a toy electric railway, on a piece of tin, 
and, placing the tin under the water, I fixed two sheets 
of glass, one inch apart, so that they were supported on 
the sleepers. A dace introduced between the sheets of 
glass soon rested on the bottom, and reflected each 
single sleeper on its body, as shown in the photograph. 
To demonstrate how the dace reflects the tone and 
colour of his surroundings, I constructed a wooden tank, 
with one side of glass. The first illustration of this tank 
shows a dace in the centre, lighted from above and from 
in front. The photograph of the dace taken by this 
illumination shows it as a silvery sided fish against a 
dark background, for the light reaching the side of the 
fish through the plate glass and eighteen inches of clear 
water is reflected back; the other side of the fish was 
dark, reflecting the dark back of the tank. 
Next, I nailed a rug on the rail above the glass, and 
carried it over the camera. The glass side of the tank 
was now as dark as the wooden side, and the dace seen 
from under the rug appeared by reflection dark against 
the dark background. From the two illustrations of the 
dace, photographed in the wooden tank, it will be seen 
that the dark fish, illuminated only from above, as in 
nature, is much less conspicuous than the silvery fish. 
Do fish conceal themselves by reflection in a similar 
manner in their native element? A glance at the 
photograph of the two dace swimming free in the obser- 
vation pond shows how, by reflecting the shade of the 
