CONCEALMENT AND COLORS IN CRUSTACEA—MINKIEWICZ. 469 
the size of the pieces of paper, and their quantity must be absolutely 
identical for the two colors, so that all the conditions will be exactly 
the same and no secondary influence may vitiate the result. 
For the same reason, the pieces should not be so large or so numer- 
ous as to conceal the bottom of the aquarium. 
These preparations made, the crabs are left in perfect quiet, an 
absolutely necessary precaution. 
After a little while (the lapse of time, however, being very vari- 
able), sometimes at the end of a quarter of an hour, the crabs will 
be found covered with little bits of paper; if everything has been 
normal, the physiological state of the crabs, the temperature of the 
water, etc., they will have chosen the pieces presenting the same color 
as the surroundings. If the walls are white, they will be covered 
with white only; they will take neither green, nor yellow, nor black; 
if the walls are green, they will be clothed only in green. 
As a control experiment, the crabs are put into two aquaria, differ- 
ently colored and placed side by side, or else the color of the aqua- 
rium is changed, leaving in it the same crabs and placing in it the 
same bits of paper. The results are then very striking, the color 
of the costume always corresponding exactly with that of the envi- 
ronment. There is perfect instinct in all its admirable teleology! 
Thus it is shown that these are Arthropods which distinguish 
colors and, still more important, distinguish all colors.¢ 
It can not be questioned, since I have established the objective 
proof, furnished by the covering, that corpus delicti found each time 
on their backs. 
Thus the very long discussions in regard to the choice of colors 
among the Arthropods may be closed. 
I am certain that similar proofs could be established regarding 
other animals. I can already point out two of them: The movable 
dwelling of the Pagurids and the burden of the Dromiids. 
My experiments on these animals having scarcely begun, I can at 
present only assert the possibility of solving the question, the Pagu- 
rids living very well in tubes of colored glass, and the Dromiids 
taking voluntarily on their backs pieces of colored material. 
It may be possible to increase the number of these cases. The 
question is worthy of the attention of biologists. 
Returning to our Maja, it is to be remarked that the process is 
not so simple as one might think at first sight. Positive results are 
not easy to obtain. But this I dare affirm after all that I have seen in 
4Tt has been impossible for me to determine absolutely whether they can 
distinguish yellow from green, in spite of the often repeated experiments but 
that is the case with the Pagurids, the Linews, and other animals, which dis- 
tinguish them most clearly, better than we do, 
