THIRTEENTH ANNUAL .REPORT 95 
One of the large floor pools contains twelve specimens of the 
striped bass (Roccus lineatus) which have never been moved 
since they were first placed in the pool fifteen years ago. This 
pool is lined with white tiles, and all the specimens are pale and 
colorless while their characteristic stripes are scarcely noticeable. 
The only normally colored fish in the lot is blind, and it is also 
undersized, since it has never been able to secure its full share of 
the daily supply of food. 
Another white-tiled pool contains skates and rays, all of 
which became pale and colorless within two days of their cap- 
ture, and ceased to exhibit their original rich brown tones. A 
newly arrived specimen is remarkably conspicuous when placed 
among them. The changes of color depend upon the eye. 
In ali these northern fishes, which reflect the tone of their sur- 
roundings, the changes are slow, requiring days or even weeks, 
but the color changes of tropical species are sudden, or actually 
instantaneous. 
A year ago the following label was attached to all tanks con- 
taining fishes subject to quick changes in appearance : 
“This species may change color at any moment. 
A few minutes’ observation of the fish is usually enough to reveal a 
change either in color or in pattern of marking. 
The color cells of the inner skin are under the instant control of the fish. 
Under natural conditions the changes of color are made chiefly for the 
purpose of concealment from enemies. They are also used for the capture 
of prey, for signaling, warning, mimicry, courtship and other purposes.” 
Through the agency of the label many of the visitors to the 
Aquarium learned to detect the changes, and found a new en- 
joyment in watching the more showy species. 
The methods by which fishes produce changes in appearance 
are well understood. The color cells in the skin are contractile, 
and, as they may contain red, blue, yellow, or other pigment, the 
different coiors result from muscular action upon oue or more 
kinds of cells. 
The fishes of tropical seas are usually of brilliant coloration, 
perhaps more so than tropical birds or butterflies, but their re- 
markable colors are not so well known, as they persist only dur- 
ing life. Outside of the tropics these fishes are to be seen no- 
where, except in a few public aquariums. 
Six months ago I began a series of daily observations on their 
colors, which have been continued to the present time. While 
the present article is merely a preliminary account of the be- 
havior of certain tropical fishes with respect to the display of 
color, enough has been learned to show that many of those under 
