ADAPTATION OF OYSTER TO CHANGES IN SALINITY 
357 
tests. The activity in this salinity was only slightly less rapid than that recorded 
in series I, when a salinity of 14.60 parts per mille was employed. A salinity of 
about 13 parts per mille appears to be but little more favorable than a salinity 
of about 10.5 parts per mille as studied in series IV and V. In the latter cases, 
however, the specimens were not able readily to recover from the harmful effect. 
This specimen quickly became adapted to a salinity of 25.53 parts per mille, 
and in spite of the fact that it had been in the water of lower salinity for 8 days it 
recovered completely within 2 days. The progress of adaptation in this case is one 
of the best examples obtained, and a graph (fig. 10) is reproduced showing all of 
the 5-minute values of S and F. After the first 2 hours, during which the valves 
were not wide open and almost no water was pumped, the shell consistently opened 
wider and the rate of flow of water increased. It may be noted that considerable 
adaptation took place overnight between recordings of the 2 days. Tins graph 
suggests also the close correlation between degree of openness and rate of pumping. 
o - - — ■ ■ — — — » — — 
Figure 10.— Adaptation of S and F (5-minute values) to salinity of 25.53 p. p. m. following change from 12.93 p. p. m. Series II. 
17°-19° C. The value, i, is shown by a broken line for reference. 
In many cases of adaptation it is difficult to determine whether the rate of 
pumping at any time is due to the rate of activity of the gills or to the degree of 
openness of the valves, which thereby determine how much water may be pumped. 
By plotting the values obtained during the 2 days when the specimen was in water 
of a salinity of 25.53 parts per mille, to show the correlation between S and F 
(fig. 11), it was clearly shown that the points, with a few exceptions due to the initial 
effect of the change in salinity, fall into definite alinement; that is, the relationship 
between rate of flow and degree of openness was the same on the first day, when 
the specimen was beginning to become adapted, and on the second day, when 
adaptation was almost complete. This is interpreted as direct evidence that adapta- 
tion in this case was entirely under the control of the adductor muscle, regulating the 
