354 
BULLETIN OF THE BUREAU OF FISHERIES 
that the gills were able to pump at the previous rate, even though the valves were well 
apart. 
These tests occupied 10 days, during which time the specimen was highly active 
and adaptable. At about noon on the tenth day (series IV, table 1) the salinity was 
reduced to 10.59 parts per mille and a few records kept during the rest of the day. 
However, the shell remained almost entirely closed. On the next 2 days kymograph 
records were not made, for the valves were only slightly open and no water was 
pumped. On the third day the valves had opened wider and the activity was recorded 
on the kymograph. Only occasionally was a little water discharged either on this 
day or during the entire 20 
days that water of this sa- 
linity was used. After the 
first few days the valves were 
generally open to a normal 
degree, and consequently it 
was the gills themselves that 
failed to function. The tests 
were continued for as long 
as 20 days with the hope that 
some indication of adapta- 
tion of the gill mechanism 
would appear. 
In an attempt to locate 
as exactly as possible the 
minimum salinity required 
for functioning of these or- 
gans, the salinity was then 
raised slightly to 12.94 parts 
per mille and maintained for 
4 days. Results being similar 
to those in the preceding 
tests, the salinity was again 
raised to 15.01 parts per mille 
for 2 days, but without any 
indication of increased ac- 
tivity. Even when the sa- 
linity was raised to 27.92 
parts per mille the specimen 
did not show any sign of re- 
covery. It only remained 
abnormally wide open, as it has been during many days in water of low salinity. 
It was clear that subjection to a salinity as low as 10.59 parts per mille for a con- 
siderable period of time had done some damage which was not readily repaired even 
after restoration of more favorable conditions. In fact, it was only after the speci- 
men had been in running sea water for about 2 weeks that it appeared to pump a 
vigorous stream of water. 
Incidentally, the behavior of the oyster during all tests after the introduction 
of the low salinity was different from the normal in that the quick, partial closures 
Figure 7.— Adaptation of S and F (5-minute values) to salinity of 36 p. p. in. follow- 
ing change from 28.06. Series IV. 17°-19° C. 
