ADAPTATION OF OYSTER TO CHANGES IN SALINITY 
353 
able to produce a slight flow of water. On the fourth day the valves were 
abnormally wide open, gaping, although the gills were able to function and 
produce a slight current. Tests would have been continued ’save ,that_gaping is 
generally indicative of loss of 
tonus of the adductor muscle and 
death of the organism. However, 
the oyster was placed in running 
laboratory water, where, after 
some days, it apparently recov- 
ered completely. 
SERIES IV 
The experiments described 
above suggest a marked sensitiv- 
ity of the oyster to lowered salinity, 
while the effect of raising the 
salinity is very temporary. In one 
case (series I) the salinity was low- 
ered to 14.60 parts per mille and 
the specimen did not become com- 
pletely adapted even after 5 days. 
It is of importance to know approx- 
imately the lower salinity limit at 
which the oyster is able to feed, for 
in nature the species is frequently 
subjected to water ranging in salin- 
ity from almost pure ocean water 
to fresh water. Before making 
such an experiment this speci- 
men (series IV, table 1) was 
tested for 2 days in water of 
a salinity of 28.06 parts per 
mille, after which the salinity 
was raised to 36 parts per mille 
and left for 2 days while records 
were kept to show the progress 
of adaptation. 
The results of this change 
to higher salinity are in har- 
mony with other similar changes 
already described (fig. 7), for the 
specimen became completely adapt- 
ed within a few hours, altlxmgh 
the initial effect of the change 
was to reduce the rate of pumping 
almost to zero. When the salinity was then reduced to 28.17 parts per mille (fig. 
8) adaptation during the first few hours was rapid, but it was not until the third day 
Figure 6.— Graph of 5-minute values of S and F showing progressive 
adaptation to salinity 28.04 p. p. m. following change from 39.10 p. p. m. 
For reference the value, 6, is shown as broken line. Series III. 17°-19° C . 
