470 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
the course of two years of research, that if the results are negative 
or undecided, it is because the animals are disturbed by secondary 
causes, which it is necessary to find and to eliminate if possible. 
There is one inconvenience about the material employed, certain 
papers, like red and blue, being quickly and almost completely 
changed in color by sea water. In these cases I have used success- 
fully some coarse paper placed in the water several days in advance 
in order to soften it and to make it sink. 
§ 2. THe HABITAT ACCORDING TO THE COVERING. 
The crabs are put into two preparatory aquaria of different colors, 
each aquarium containing material for concealment of the same color. 
Another aquarium is divided in halves, each half corresponding in 
color to one of the preparatory aquaria, and the crabs are trans- 
ferred to it after they have clothed themselves in the preparatory 
aquaria. 
The crabs are then invariably seen to make their way toward the 
half of the aquarium corresponding in color to their covering, re- 
maining there a long time. Thus, for example, in the aquarium red- 
green, the red crabs go toward the red end, the green crabs toward 
the green one. 
The most surprising experiment was one that I made in an aquarium 
divided into three equal parts, the middle white, the other two black. 
The white crabs reached the central part (white) and stayed there 
during the time of the experiment (several hours). The control 
experiment in the aquarium white-black-white gave me the same 
result for the black crabs. 
These last results are all the more striking, as it is a well-known 
fact that crabs rest normally in crevices, having, as is said nowadays, 
a thigmotropism (Jennings=stereotropism of Loeb), that is to say, 
taking a regular position (++) in contact with solid bodies. 
The experiments I have just described in paragraph 2 are perhaps 
more difficult to perform than those described in. the preceding para- 
graph, because the crabs, upon being transferred from one aquarium 
to the other, are usually much excited and consequently in an ab- 
normal physiological state. This must be taken into consideration 
if one has not attained definite results. 
What marvelous instinct, is it not, of active variable mimicry, if 
we would employ the Darwinian expressions in use, although to my 
mind too anthropomorphic! Or, indeed, if we go a little further in 
the psychological and determinate path, it would be rather conscious 
choice, perhaps even deliberate, carried out with premeditation, ete. 
For myself, I prefer the new expression, instinctive synchromatism, 
containing nothing but the statement of the facts, with no explana- 
tion, mechanical, selective, or psychological. I prefer this definition 
