348 
BULLETIN OF THE BUREAU OF FISHERIES 
The nature of the results and the different lengths of time during which specimens 
were subject to water of different salinities make it impossible to present the data 
obtained in any manner other than by description of the tests with each specimen. 
Seven such series are described below. 
SERIES I 
This was the first specimen on which detailed experiments were performed. 
The salinity at the beginning was 29.40 parts per mille and records were kept for 
thirty -seven 5-minute periods, or 185 minutes. Then, on the same day, the salinity 
was lowered to 26.96 parts per mille and the activity recorded for the next 205 
minutes, or forty-one 5-minute periods. The records taken at the two salinities 
(table 1, series I) are closely similar, although the averages in the former case are 
S, 8.53; F, 6.45; and in the latter case, S, 7.13; F, 5.40. Obviously the results are 
inadequate for comparison because of the short duration of exposure to each medium. 
On the following day the salinity was lowered still further to 24.03 parts per 
mille and records kept for forty-seven 5-minute periods. The low F values during 
early treatment at this salinity, as shown in the table, indicate a marked effect of the 
change, though later values appear to be in harmony with those obtained at the 
original higher salinities. 
The effect of lowering the salinity is more strikingly shown in the tests of the 
next 2 days (Nov. 9 and 10), after changing the salinity from 24.03 to 17.76 parts per 
mille. Although during the first day the shell remained approximately as wide 
open as previously, only a feeble stream of water was pumped by the gills. In figure 
1 the consecutive 5-minute values are shown graphically, to illustrate the slow 
Figure I.— Values of Sand F showing adaptation during 3 days to a salinity of 17.76 p. p. m. following a change from 24.03 p. p. m. 
Series I. 17°-19° C. 
adaptation of the gill mechanism (F) while the valves (S) quickly recovered their 
normal degree of openness. It is doubtful that adaptation was completed even after 
more than 2 days. However, the salinity was changed (Nov. 11) to 28.50 to test 
adaptation to a rise in salinity. Records were kept on the first day for fifty-four 
5-minute periods. Wit hi n a very short time after the change, the values of F rose 
almost to normal, though not until the next day did the shell open wide enough to 
permit completely normal gill activity. 
After the specimen had been in this water for 4 days the salinity was again low- 
ered to 22.20 parts per mille. Adaptation to this change was relatively rapid, 
