934 THE AMERICAN NATURALIST. [VOL. XXXV. 
place the aquarium with the crayfish in diffused light and 
to allow them to become accustomed by degrees to changed 
conditions. 
Some very good results were obtained in these experiments. 
Crayfish in black, blue, and green colors were changed to brown 
and red under the influence of light. These color changes, 
however, were very slow. Several months were required to 
produce distinct changes. 
Other experiments were made in the laboratory upon the 
influence of environment on the color of the crayfish. A num- 
ber were taken from different places where they were of 
various colors and kept for some time in an aquarium. This 
aquarium tank was made of zinc and was partly covered to. 
exclude the light. In some cases very distinct color changes 
occurred. This was especially true of those which were red 
and black. Out of a large number of crayfish of different 
colors which were kept in this way for several months, nearly 
all were changed to the same gray color of the zinc aquarium. 
An.excellent illustration of color changes is furnished by 
another species, Cambarus diogenes. These may be found in 
any of the smaller streams. In the early spring they vary 
much in color, but later in the year nearly all are red. The 
explanation here lies in the habits of this species. They 
burrow during winter and come out in the spring with more 
or less of the color of the soil. These colors are gradually 
turned to red in the open sunlight. There has been no oppor- 
tunity for observations upon other burrowing crayfish, but 
what is true of diogenes is no doubt true of other species 
which burrow in winter. 
Some little time was also spent in studying color changes in 
the young crayfish. This study was made during the months 
of April and May of the present year, and was confined to one 
species, immunis. The young of immunis are at first red. 
This red color, however, is not apparent to the unaided eye. 
The pigment layer of a young crayfish consists of a number of 
large chromatophores which lie directly below the chitinous 
integument. These color bodies are somewhat scattered, and 
the little color they give is scarcely noticeable in comparison 
