700 ZOOLOGICAL 
FIGURES 3, 4 and 5 ARE DIFFERENT VIEWS OF A SINGLE FISH, THOUGH A 
DIFFERENTSPECIMEN FROM THAT SHOWN IN FIGURES 1 AND 2. 
a black bottom and a very pale shade upon a 
white bottom, but exhibited one color pattern 
upon sand (Fig. 1), another upon fine gravel 
(Hig. 2), and yet another upon a bottom of small 
stones. A number of entirely artificial bottoms, 
such as variously painted strips of glass, were 
also employed in these experiments, sometimes 
For example, 
the skin patterns were found to vary both with 
the relative amounts of black and white in the 
background, and with the degree of subdivision 
of the areas of the latter. Comparison of Fig- 
ures 3 and 4 will illustrate this point. 
Now this capacity of the fish to adapt itself 
with rather surprising results. 
to different backgrounds, although at times very 
striking, was restricted within certain definite 
limits. In general, brilliantly colored back- 
grounds seemed to be beyond the fish’s power of 
imitation. The animal ap- 
peared to be limited almost aac ar a 
wholly to the black, white, ve 
gray and brown of its cus- 
Then, too, 
the creature was found to 
possess permanent spots and 
markings, due to the special 
tomary habitat. 
grouping of the pigment 
cells in its skin.* These 
*The color changes of fishes 
are due to the movement of the 
pigment granules within the 
chromatophores, or color cells, 
under the influence of stimuli 
transmitted through nerves. The 
chromatophores themselves 
probably do not change either 
in shape or position. 
SOCIETY 
BULLETIN. 
proved to be fixed morpho- 
logical structures, however 
much they might vary at 
different times in their rela- 
tive intensity. Even when 
the fish was adapted to a 
perfectly uniform back- 
ground, the outlines of these 
spots were for the most part 
dimly visible, and when they 
reappeared they always had 
the same form and occupied 
the same position. Under 
such circumstances, we could 
not reasonably expect that 
squares, cross-bands, circles, 
ete., should be copied in any 
true sense by the fishes, and 
as a matter of fact they were 
not. 
This power of adaptation was best shown 
upon such backgrounds as formed a part of the 
natural habitat of the species. It was not, 
however, restricted to such cases, but the pig- 
ment was at times disposed in ways which, it is 
safe to say, were quite foreign to the previous 
experience of the race. For example, the near- 
ly white and perhaps also the darkest condition 
attained by the fish, likewise the vividly con- 
trasted black-and-white condition, without in- 
termediate shades (Figures 3 and 5) which was 
assumed by certain specimens upon some of the 
artificial backgrounds. Thus, the notion that 
the fish is limited to a few stereotyped responses, 
representing the most familiar types of habitat, 
must be rejected at once. 
The individuals used differed greatly in their 
powers of adaptation, and some seemingly nor- 
ne = 
as 
* 
anette = ae sate 
Fic. 4. 
SAME FISH AS IN FIG. 3, ON A DIFFERENT BOTTOM. 
" Pras bh’ 
