468 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
The proceedings are the same if the crabs are furnished with 
sponges, hydroids, or compound ascidians instead of alge. If they 
do not find living material they content themselves with débris, with 
pieces of the carapace of dead Crustacea, with shells—in fact, with 
anything that they may find, paper, rags, threads, ete. 
The species which we dredged on board the Roland having come 
from different bottoms and different depths, varied correspondingly 
in their method of disguise, especially in regard to color; and it is 
this very fact which suggested to me the idea of undertaking some 
investigations in regard to the question 
of the relation between the color of the 
covering and that of the environment. 
The material suitable for these ex- 
periments I found indicated in this pas- 
sage by M. Hermann Fol:¢ 
I tried once to take away from it (Maja) 
all the weeds it might have taken for cut- 
tings, and to give it instead bits of hay and 
of white paper. It conscientiously stuck on 
its back these objects, which could only serve 
to make it still more conspicuous than if it 
had put nothing there at all. 
Fic. 7—The same movement seen | decided, therefore, to use colored 
from the ventral side. (AH. a i 5 
ee, oe ee paper, and employed a fine paper called 
papier de sole. 
The crabs behaved in regard to this material just as if it had been 
an Ulva (U. lactura Linneus). 
III. HXPERIMENTS MADE IN AN ENVIRONMENT OF VARIABLE COLOR. 
§ 1. THE COVERING FOLLOWING THE ENVIRONMENT. 
The best preparation for experiments, of which I have made hun- 
dreds, is the following: : 
In an aquarium constructed entirely of glass, the bottom and the 
sides to a certain height are covered with colored paper pasted to 
cardboard, so that too much light may not pass through, as the 
crabs have a strongly marked negative phototropism; they are photo- 
phobes, in the psychological language of Vitus Graber and others; 
that is to say, they avoid the direct light, as well as fire screens and 
light places. There are then placed in the aquarium a few thor- 
oughly cleaned crabs, not more than two or three, and some pieces 
of two kinds of papier de soie—one the same color as the environ- 
ment and the other any different color, no matter what. The shape, 
74H. Fol; Linstinct et Vintelligence. Rev. Scient., 3° série, No. 7 (1886). 
