ZOOLOGY: W. H. LONGLEY 61 1 
blanching appears, and the darkening of the crab in it was therefore 
delayed. 
It does not seem to be true, as has been suggested by Dr. Cowles, 
that the "blanching of individuals on the sands of Loggerhead Key 
is probably due to high temperature alone/' or that during a large part 
of the time Ocypoda would be heat-blanched rather than adaptively 
colored.. He observed that water standing outside the laboratory was 
heated to 45°C., at which temperature experiment shows that the 
substratum exercises a neghgible effect in determining the crabs' colora- 
tion. Even higher temperatures than that recorded may occur, but 
this fact has only a sKght bearing upon the matter at issue, for this 
excessive heat does not characterize the creatures' environment when 
they are exposed. 
The animals live and feed largely in the zone below high water mark, 
where actual observation twice showed a temperature of 39°C. when the 
same thermometer lying flat in the same way on the sand 25 feet above 
it registered 49° and 45° respectively on the two occasions. It may 
also be demonstrated readily by raising the instrument half an inch 
on crotched sticks that the temperature prevailing at the level at which 
an active crab's body would actually be is considerably lower than 
on the sand, being 37° and 36.5° in the two cases cited. That is to 
say, at the hottest time in the day the temperature throughout the 
normal range of active crabs is very little above the minimum at which 
heat-blanching occurs. But at these times very few crabs are out of their 
burrows: five were digging them or standing idly in their mouths in the 
first case and only one in the second, while none at all were moving 
about freely over the sand where dozens might be seen both earlier and 
later in the cooler parts of the day. It is clear, therefore, that, unless 
their reactions to air and water temperatures are not the same, when the 
animals are actually exposed to the attacks of enemies, temperature 
is not sufficiently high to inhibit the effect of the substratum in induc- 
ing adaptive color changes which might reduce their conspicuousness. 
So far it is apparent that the inference that adaptive color changes 
occur in the species mentioned rests wholly upon the demonstration of 
their ability to effect such changes in the laboratory. Similar adjust- 
ments are made, however, under natural conditions. It was, indeed, 
observation of the fact that, as one walks along a beach on which there 
is striking contrast between the dark and light patches covered by shal- 
low water, the individual young Callinectes marginatus and ornatus that 
dart away from under foot differ in shade according as they start up 
from one or the other, that attracted attention to the possibility that 
such relations exist as have been reported in this article. 
