No. 4.— Studies from the Newport Marine Zodlogical Laboratory. 
XXIX. 
Preliminary Note on some Modifications of the Chromatophores of Fishes 
and Crustaceans. By ALEXANDER AGASSIZ. 
In a former paper on the Development of Flounders,! I have called 
attention to the rapidity with which young flounders adapt themselves 
to their surroundings, and have shown how soon their pigment cells, 
when young, assume in a general way the coloring of the bottom on 
which they rest. I have since that time experimented occasionally upon 
the effect of a black and of a white bottom upon other fishes, and upon 
Crustacea in the young stages of which there were huge or highly 
specialized pigment cells (chromatophores). 
I was surprised to find that in adult specimens of Gasterosteus, for 
instance, the coloration was soon modified by keeping the fish upon a 
black or upon a white tile. A number of Gasterosteus were taken 
which showed but slight individual differences, and might have passed 
as presenting no perceptible contrast in their general coloring (Figs. 1, 2). 
They were divided into two sets, each set placed in a glass dish, one 
upon a bottom of black tiles, the other upon white tiles. 
At the end of three days, there was already a very striking contrast 
between the coloration of the two sets of specimens. Those placed 
upon the black tiles had retained their original coloration, while those 
upon the white tiles assumed a grayish tint. The pigment cells of the 
darker bright-colored specimens consisted of two kinds of chromato- 
phores, fully expanded (Figs. 1, 2). The uppermost cells were highly 
dendritic, with closely packed thin ramifications of a dark chocolate 
color, with nearly black nuclear centre ; the lower chromatophores were 
more compact, with flatter and spreading ramifications a short dis- 
tance from the centre. In the specimens which had become bleached, 
on the contrary, the chromatophores were reduced to mere dots, with 
1 On the Young Stages of Bony Fishes. By Alexander Agassiz. I. The 
Development of Flounders. Proc. Am. Acad., Vol. XIV. p. 1. Boston, 1878-79. 
VOL. XXIII. — wo. 4. 
