358 
BULLETIN OF THE BUREAU OF FISHERIES 
valves, while the gills themselves become adapted quickly. In this respect these 
results are entirely different from those obtained in series IV and V, in which, after 
the salinity was raised following treatment in about 10.5 parts per mille, the shells 
Figure 11.— Relationship between S and F during the first (solid points) and second (open circles) days following change in 
salinity from 12.93 p. p. m. to 25.53 p. p. m. Series II. (See fig. 10.) 
remained wide open but the gills were inactive. Between 10.5 and 13 parts per 
mille, then, there is a tolerance limit, below which there appears to be a destruc- 
tive effect. 
