214 
ZOOLOGY: S. O. MAST 
There is clear evidence of the submarine solution of a thickness of 
about two feet of limestone in the middle region of the Maer Island reef 
flat between 400-1600 feet from shore; but this may be chiefly due to 
the carbon dioxide washed outward from the densely forested shores 
of the Island during the rainy season, and not to the sea water as such. 
Indeed the experiments and observations of Dole, and of Vaughan 
would lead to the conclusion that the sea water of coral reef lagoons lacks 
free CO2 and is therefore probably incapable of dissolving limestone. 
All species of reef corals survive without apparent injury an immer- 
sion for 4 to 5 hours in sea water diluted with an equal volume of rain 
water, and many species can withstand 11 hours of this treatment, 
and thus it appears that even torrential rains cannot be an important 
factor in the destruction of the reef flat corals of Maer Island through 
dilution of the water, for the tidal range is about seven feet and the 
incoming sea water would soon offset any dilution due to rains. 
The injurious effects of rains upon coral reefs is due solely to the silt 
which they cause to be washed outward over the flats. 
The research of which the above is an abstract, will be published by 
the Carnegie Institution of Washington. 
CHANGES IN SHADE. COLOR AND PATTERN IN FISHES AND 
THEIR BEARING ON CERTAIN PROBLEMS OF 
BEHAVIOR AND ADAPTATION 
By S. O. Mast 
ZOOLOGICAL LABORATORY. JOHNS HOPKINS UNIVERSITY 
Presented to the Academy, February 3, 1915 
It is well known that the surface of many organisms is in appearance 
much like their environment. That is, the organisms simulate their 
surroundings and consequently are more or less inconspicuous. In 
some of these organisms the characteristics which produce such simu- 
lation are fairly permanent and the creatures correspond in appearance 
with, what may be termed, the general average of their environment. 
In others these characteristics may change rather rapidly, in such a way 
that the animals appear almost continuously like their surroundings, 
no matter how much they may change. These phenomena have al- 
ways excited a lively interest in naturalists and a great amount of work 
has been done on them. They have been particularly prominent in 
discussions bearing on evolution and consequently most of the investi- 
gations concerned questions of function and origin and development, 
both individual and racial. 
