610 
ZOOLOGY: W. H. LONGLEY 
Euryplax nitida Stimp., all of which as well as those mentioned above 
have perhaps been overlooked because they are much less apparent in 
mature than in immature specimens. It is also clear that in O. arenaria 
as well as in the six species last enumerated, the shade of the substratum 
plays a very important part in determining that of individuals rest- 
ing upon it, since in each within a few minutes, usually less than ten, 
at temperatures commonly prevailing in the laboratory it is possible 
to reverse the shade of the two members of an adapted pair simply 
by transferring each to the dish occupied by the other. 
Light colored crabs, essentially white ones, may be cooled in white 
dishes from temperatures between 30° and 35°C. to 12° and be com- 
pletely paralyzed by the cold without changing in the least in shade. 
Crabs whose shade is adjusted to that of light and dark colored dishes 
respectively may be transposed at a temperature at least as low as 
16°C. and have their coloration reversed as definitely as under warmer 
conditions. Cool crabs in dark dishes may be heated to approxi- 
mately 35°C. before they commence to show any effect of the treat- 
ment. At higher temperatures, which vary in individual cases, they are 
blanched. At such temperatures it is also impossible to induce dark- 
ening, or at least the development of a distinct pattern, by transposing 
a light crab to a dark dish. Hence it is apparent that temperature is 
not the basic factor concerned in the matter, but merely one that 
limits adaptive color changes in Ocypoda near the upper level at which 
it is able to survive. It is possible, indeed, that the very appearance of 
heat-blanching indicates the abnormahty of the situation, for, regard- 
less of the shade of the substratum, a similar effect follows when 
the water in which the crabs are is charged artificially with CO2. 
The degree to which Ocypoda's coloration is independent of tempera- 
ture may be demonstrated most strikingly in a single experiment by 
transposing specimens which have been standing in cold white dishes 
and warm black ones respectively. In a specific instance the colora- 
tion of two crabs was reversed without that one which was turning 
from dark to light ever becoming warmer than 17°C., or the other cooler 
than 35°. Equality of shade was attained in twenty-nine and com- 
plete reversal in about fifty minutes. Thus it is plain that temperature 
is so much less effective than the shade of the underlying bottom in 
determining coloration that the latter is able to induce adaptive changes 
in opposition to Cowles's laws in the face of a temperature difference of 
not less than 18°C. The time relation established, however, does not 
represent the minimum required to effect the change, since the water 
in the dark dish was for a time above the temperature at which heat- 
