478 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
But hydratation is not necessarily united with janthinotropism of 
Lineus, nor dishydratation with erythrotropism, as might be inferred 
from the statements of G. Bohn.¢ 
The following facts show this well: 
1°. The inversion of the chromotropism of the Nemerteans, appear- 
ing the second day, continues generally two days and disappears the 
fourth. The animal becomts normal—erythrotropic. 
2°, After having lived during two or three weeks in my solutions 
(sea water with distilled water), and presenting consequently their 
normal chromotropism (erythrotropism), the Zineus changes again 
when it is transferred to pure sea water and become janthinotropic. 
It would seem to be therefore rather the disturbance of the physi- 
ological equilibrium which provokes the inversion of the tropism, a 
fact which agrees well with my recent experiments on the Pagurids. 
Let us leave a normal and chlorotropic Pagurid in a square, bi- 
colored basin, of one to two liters, without changing the water. 
Let us try from time to time its chromotropism by putting it on the 
line dividing the two colors. 
A few days afterwards we shall see the animal gradually intoxi- 
cated by the products of its excretions, change the type of its chromo- 
tropism and become clearly erythrotropic (and negative with regard 
to the white screens). The scale of tropic values of the different 
colors remains the same, but it diminishes toward the green and 
white, the negative action of which is strongest, according to the 
formula: 
(+) black — red <— yellow — blue <— violet — green <— white (—). 
Thus, on the green-violet background, the Pagurids proceed toward 
the violet, though they are negatively phototropic and erythrotropiec, 
which again confirms the relative autonomy of the tropic actions of 
the different hght radiations. 
The results essential for us are: 1°, that the change of chromo- 
tropism is no longer a possibility a priori, but a concrete fact, experi- 
mentally established; 2°, that the disturbance of the physiological 
equilibrium, which determines the changes, can be provoked by the 
most diverse agents. 
VIII. THE VARIABLE CHROMOTROPISM OF HIPPOLYTE AS A NORMAL 
PHENOMENON, ACCOMPANYING SYNCHROMATISM. 
Is it not possible that among the agents which provoke the altera- 
tion of the chromotropism may be also found the luminous agents 
and especially the chromatic properties of the surrounding medium ? 
“@G. Bohn: Attractions et oscillations des animaux marins littoraux sous l’in- 
fluence de la lumiére. Mém. Inst. gén. psychologique, t. I. 
