480 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
This phenomenon, which the English authors term choice (power 
of selection), is only chromotropism, but very complicated, very 
much differentiated, and as it were, individual. 
For this phenomenon I have proposed the objective name of syn- 
chromatic chromotropism, a name well describing its specific char- 
acter. 
What, then, are these chromatic varieties of Hippolyte, having 
each its synchromatic chromotropism ? 
In the third memoir by Keeble and Gamble,* in the chapter en- 
titled “ Sympathetic colouration,” we read that the young individuals, 
still colorless, or nearly colorless, rapidly assume the coloration of 
the algze upon which they are placed. 
What is still more interesting is, that not only young colored indi- 
viduals, but also adults which have been transferred to backgrounds 
of another color, readily change their initial coloration and assume 
a new one, which is exactly that of their environment. 
The following are the principal results of the experiments that I 
performed on this animal at Roscoff in 1906-7: 
1°. I obtained numerous Hippolyte of the following colors: 
A. Simple colors; that is to say, in which the corresponding pig- 
ments are only dilated: (a) Red, dark and light; (0) yellow, dark. 
light, and whitish; (¢) blue and bluish (transparent). 
B. Composite colors: (d) Orange (yellow pigment-+-red pigment) ; 
(e) green, lemon and olive (yellow pigment-+-blue pigment in dif- 
ferent mixtures) ; (7) violet, dark and lilac (red pigment--blue pig- 
ment). 
Without counting the usual colors—green, brown, and brownish 
(the last two composed of red pigments+-yellow+-blue). 
Thus I obtained all the fundamental colors of the solar spectrum 
with numerous shades, corresponding always to the color of the paper 
used. 
It is surprising to find in the above results the bright colors, yellow, 
blue, and violet, which are not met in the natural environment of 
HHippolyte as it fee among plants and alge. 
It must be deduced from this fact that the extent of the chromatic 
plasticity of Hippolyte is not due to natural selection, that it is of 
primary origin, and depends directly upon the chromatic agents of 
the environment. 
2°. Every chromatic variety, whether natural or obtained experi- 
mentally, can be changed into any other. 
3°. The intensity of the colored hght plays a much less important 
part than its chromatic equation; this may be concluded, at least, from 
“Keeble and Gamble: the colour physiology of higher Crustacea. 38. Phil. 
Trans,, series B, vol. 198. 
