ADAPTATION OF OYSTER TO CHANGES IN SALINITY 
355 
which occur with characteristic frequency in a normal specimen almost never were 
to be observed. The oyster acted almost as if anaesthetized, although the shell 
varied considerably in degree of 
openness. All movements, however, 
were slow. Nevertheless, secretion 
of shell proceeded at a rapid rate, 
and when the experiment was dis- 
continued several millimeters of 
thin new shell had been added to 
the margins of the valves. 
SERIES V 
In the 
series the 
a salinity 
preceding 
specimen was left in 
of 10.59 parts per mille for 20 
days, resulting in damage to the 
pumping mechanism. It was de- 
sirable to know whether shorter 
exposure to such a salinity would 
have the same harmful effect. 
A specimen was therefore tested 
thoroughly for 2 days in water of 
high salinity (27.35 parts per mille), 
during which time it reacted favor- 
ably, pumping vigorously (series 
V, table 1). After being changed 
to a salinity of 10.64 parts per 
mille, the valves remained at lirst 
only slightly open but during the 
next 2 days opened abnormally 
wide. As in the previous series, 
almost no water was pumped. 
After 4 days of treatment, the 
salinity was raised to 27.39 and 
records kept for 5 days. Within 
about 2 hours after the change the 
gills began to pump a small stream. 
Beyond this, however, there was 
no further recovery during the 5 
days. The shell opened wider and 
wider, but never was more than a 
feeble circulation of water produced 
by the gills. 
The results are similar to those 
described in series IV, with the 
Figure 8. — Five-minute values of S and F during adaptation to a salinity 
of 28.17 p. p. m. after change from 36 p. p. m. The value, 10, is shown 
as broken line for reference. Series IV. 17°-19° C. 
difference that in the present series exposure to low salinity had not been sufficiently 
prolonged to produce the harmful effect to as great a degree. 
