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BULLETIN OF THE BUREAU OF FISHERIES 
previous levels. (See series I, table 1.) When the salinity was then raised to 
28.56 the specimen became adapted to a comparable level within a few hours. 
SERIES II 
Preliminary tests in a salinity of 28.87 parts per mille were carried on only 
during 1 day (thirty-six 5-minute readings), although it later appeared that they 
should have been continued for several days more (series II, table 1). When the 
salinity was changed to 22.70 parts per mille for 2 days and then to 28.74 parts per 
mille, the correct level of adaptation was reached. After 3 days in the latter a 
relatively slight change was made to a salinity 25.08 parts per mille. A graph 
(fig. 3) is reproduced showing the gradual adaptation following the change. Within 
about 4 hours adaptation proceeded almost to completion, as may be seen in the 
figure by comparing the values of S and F with those of the previous day, when higher 
salinity was used, as well as with those of the following day. 
Figure 3. — Adaptation of S and F (5-minute values) following change in salinity from 28.74 to 25.08 p. p. m. Series II. 17°-19° C. 
After returning the specimen to a salinity 28.94 parts per mille for 1 day, the 
water was changed to a salinity of 17.85 parts per mille, a step considerably greater 
than that just described. During the first several days (series II, table 1) it appeared 
that adaptation was slowly occurring, but during the remainder of the 11 days there 
was no further obvious recovery. The valves did not remain open wide enough to 
permit free flow of water. Yet when the salinity was raised to 27.27 parts per mille 
recovery was so rapid that activity seemed to be almost at its normal level within 2 
or 3 hours. 
A considerable difficulty in the analysis of these data lies in the fact that two 
activities are concerned, namely, the degree of openness of the shell (S) and the rate 
at which water is pumped (F). The latter is dependent upon the former, and it 
appears that both functions are influenced independently by changes in salinity. 
However, even under constant conditions of temperature and salinity, there is a 
