ADAPTATION OF OYSTER TO CHANGES IN SALINITY 
347 
the adductor muscle, resulting in the shells remaining at almost their optimum degree 
of openness. At 20° C. or above the valves tend to become more closed, although 
the gills themselves pump more rapidly up to between 27° and 28° C. 
The salinity of the running water at the laboratory varied generally between 
26 and 29 parts per mille. Water of a lower salinity was prepared in a tank, large 
enough for several changes of water in the experimental aquaria, by mixing the 
laboratory water with pure spring water. Control tests showed this method to be 
adequate, for specimens behaved identically in bay water of salinity 28 parts per 
mille and in water of the same salinity made by mixing spring water and con- 
centrated bay water. 
The water level in the experimental tanks was marked so that occasional small 
additions of spring water prevented more than very slight changes in salinity due 
to evaporation. The pH of the water varied only slightly, between 7.7 and 8.0, 
in harmony with that of water on the oyster grounds. 
Specimens for experimentation were always kept in the running sea water of 
the laboratory for several days or weeks before use. During the first one or more 
days after being placed in the experimental aquarium, a specimen was tested in 
water of approximately the same salinity as the running laboratory sea water. In 
making a change of water, of either the same or a different salinity, the water was 
drained from the experimental tanks, which were then flushed out thoroughly with 
the new water before being filled to the correct level. To save time, the new water 
was warmed to the experimental temperature (17°-19° C.) before being siphoned in. 
Some specimens were mounted upon a base of plaster of paris and sand, while 
others were set rigidly upon a small celluloid frame. No ill effect of the plaster of 
paris was noted. 
After completion the kymograph papers were marked off exactly into 5-minute 
periods for analysis. Planimeter measurements were made of the area enclcsed 
between the record line and the reference line during each 5-minute period. These 
measurements are considered in the following descriptions as representing S (the 
degree of openness of the shell) and F (the relative rate of flow of water through the 
gills) during each 5-minute period. 
DESCRIPTION OF EXPERIMENTS 
These experiments were started for the purpose of determining whether there is 
any relationship between salinity and the rate at which water is pumped. It was 
thought that adaptation to a change in salinity would occur quite quickly, since in 
their natural environment oysters are subject to frequent and sometimes extreme 
salinity variations, and it was planned to make a change, allow the pumping mecha- 
nism to reach a stable level of activit}q then to change again. In this manner it was 
hoped that sufficient values might be obtained to permit graphical analysis of the 
relationship between salinity and the rate of feeding. 
It soon became evident, however, that such a procedure would require a long 
period of time, even with only one specimen. Adaptation was found to be extremely 
slow, and the variations in degree of openness of the valves and in rate of pumping 
are so great even under conditions of constant salinity and temperature that any 
test would have to be carried on for many days, or even weeks. It was, therefore, 
decided to attack the problem by making a study of the process of adaptation following 
changes in salinity with respect to shell movements and gill activity. 
