TEMPERATURE AND SHELL MOVEMENTS OF OYSTERS 
7 
When the results obtained with the two specimens in experiments Nos. 2 and 3 
(Table 1, fig. 1) are plotted according to time of day, a diurnal wave is produced. In 
Figure 4 the percentage of time that the specimens were open at each of the 24 hours 
of the day during the entire period (29 days) is plotted. From 4 to 5 p. m., for 
example, the oysters were open during 95 per cent of the possible 29 hours at this 
time. Similarly temperature is plotted as the average of the readings at each hour 
during the period. The resultant graph represents the records of 29 days presented 
as a single average day. The curves of temperature and percentage of time open are 
almost identical, although the average daily difference in temperature between trough 
and crest of the diurnal wave is only 2.1° C. The specimens, however, at the trough 
of the wave were open only about 50 per cent of the time, and at the crest 95 per cent. 
Were it not for the fact that the two waves are so closely similar, in spite of individual 
differences in the behavior of the oysters, it might seem that other factors, such as 
A.M. M ' p.m. 
Figure 5.— Graph showing diurnal shell activity of four oysters. The percentage of time open 
during each hour of the day over 29 days is plotted along with the average temperature hourly 
over the same period. Although the specimens are closed more than those shown in Figure 4, 
due to presence of sulphite liquor in the water, the parallel between temperature and shell 
activity is clear 
light, might be the cause of the variation. While it is probable that fight has such an 
effect and may have influenced the results to some degree, it is obvious that tempera- 
ture variation is the primary stimulating agent. 
In the same series with the above were four other specimens in dilute solutions 
of sulphite liquor, and which, because of this, did not remain open as many hours per 
day as the normal oysters. The results of these four specimens are similarly presented 
(fig. 5), for their number tends to overcome the variations due to individual differences. 
Although the curve is lower in percentage of time open, it is definitely of the same 
character as the accompanying temperature curve. While the maximum tempera- 
ture difference of the curve was 2.1° C., there was a 32 per cent difference in time the 
oysters were open. 
The relatively great effect of a small average difference in temperature, as in 
Figure 4, as compared to the lesser effect of the greater change of temperature over 
