474 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
removal of the eyes (or of the ocular nerve cords), and thus de- 
prived of all the perfection and the charm given by the photore- 
actions. It would perhaps be sufficient to conceal the crabs under 
the normal conditions of their life at the bottom of the sea, among 
alge, sponges, ete. 
It is, however, much more complicated, and the most difficult part 
remains for us to analyze. 
The problem of the choice of colors, of the existence of which we 
have given incontestable proof, cannot be solved at once. It was 
impossible to enter upon it before the discovery of chromotropism as 
a phenomenon sui generis, independent of common phototropism—a 
discovery made by myself at Roscoff in 1906. 
VI. ANIMAL CHROMOTROPISM. 
I have given this name to the kinetic reaction of animals in rela- 
tion to the action of colored rays (or screens), this reaction being 
either positive or negative, as in all other tropisms. 
It must be pointed out that I do not propose any theory of chro- 
motropism, nor of tropisms in general, the physiological nature of 
the phenomena being at present too obscure. I understand the fact, 
to which I apply the word tropism, as including only the objective 
statement, with no explanation, which would be premature in the 
present state of knowledge. 
The freshly hatched larve of Maja squinado (Zowe) present, as 
is well known, a very marked positive phototropism and heliotropism. 
I have been able to prove that they are at the same time very sensi- 
tive to the chromatic rays, that they are constantly directed toward 
the rays with the shortest wave, that is to say, toward the violet, and 
in its absence, toward the blue, etc. 
They distinguish also all the visible rays. The reaction is almost 
instantaneous: All the Zoze swarm toward the most refrangible rays 
as soon as they come under their influence. 
The phenomenon takes place not only in the horizontal glass tubes, 
but also in vertical tubes, whatever may be the distance from the 
most intense region to the surface of the water. 
The Nemertean, Lineus ruber, behaves in a very different manner. 
First and foremost, it is strongly negative with respect to diffused 
light. If the individuals are put in small square crystallizing pans, 
and colored light is made to fall upon them from only one side, it 
is found that the animals turn immediately and invariably toward 
certain rays (red, yellow: positive chromotropism), while they are 
repelled by others (blue, green: negative chromotropism), all the 
other conditions being identical in the crystallizing pans, which are 
placed side by side. 
