10 
BULLETIN OF THE BUREAU OF FISHERIES 
Figure 6.— Graphical presentation of the data given in Table 1. The circles repre- 
sent the average percentage of time the specimens were open during the several 
series, plotted against the average temperature during the same periods. The 
solid points represent the increase in percentage of time open following a 2° C. 
rise in temperature during the average daily cycle, as described in the text 
Figure 7.— Average day’s record of the percentage of time that one specimen of Ostrea 
virginic a remained open during each hour of the day during the period from October 
9 to November 30, showing the clearly defined diurnal wave of shell activity 
