NO. 419.] THE COLORS OF THE CRAYFISH. 935 
with the colors of some of the internal organs, which can also 
be seen. The color of the young crayfish should be studied 
with the microscope. The integument of the young crayfish 
is perfectly transparent, and with a microscope any changes in 
color in the chromatophores is easily observed. 
A series of observations was made upon the young crayfish 
in one pond where the old were black and in another pond 
where the old were blue. In this pond where the old crayfish 
were black the young were at first red and gradually changed 
to black. This change of color required about two months' 
time. In crayfish one or two weeks old only a very few of 
the chromatophores showed any change in color, while in cray- 
fish one month old possibly one-half of them would be changed 
in color, and in those from two to three months old the process 
of color change was nearly always complete. The integument 
remains transparent up to this age, so that all stages in color 
changes were readily seen. 
In the second pond where the old crayfish were blue the 
young, which were red at first, changed to blue, this change 
requiring about the same length of time. In other places 
where the old crayfish were red the young crayfish underwent 
no change in color. They were red at first and remained red in 
color. In this work the young crayfish of different ages were 
brought into the laboratory and examined. The color changes 
were such as occur among crayfish in their natural environment 
and under ordinary conditions. No attempt was made to keep 
them in the laboratory for the purpose of experiments. 
From these observations it will be séen that the colors of 
crayfish are due to two causes. The sunlight produces the red 
color, though this same color may be caused by the rarer: 
ment. All colors excepting red are due to the influence of 
environment. In all cases these colors serve as a protection 
against enemies. 
The greater part of this work has been confined to one 
species, Cambarns imi although some work has been done 
on three other species, propinquus, bartonii, and diogenes. 
But there seems to be no reason why similar changes in color 
should not occur among all other species. 
