TEMPERATURE AND SHELL MOVEMENTS OE OYSTERS 
13 
That light is not the factor primarily responsible for the diurnal variation in 
activity is shown by the results of a series of tests made at Galveston, Tex. The shell 
movements of two specimens in running water were recorded for 25 days. One 
specimen was in a jar surrounded by a black box which effectively blocked all ordinary 
light rays while admitting air. The other was exposed in the laboratory. Figure 10 
gives the records of the two specimens. The curves are essentially similar, showing 
that even in constant darkness the diurnal wave of shell activity is clearly marked. 
It was pointed out that there was some difference between the results of Nelson 
(1921) and those of Galtsoff (1928) with regard to the length of time oysters remain 
open daily. The former found 20 hours to be the average, the latter only 17 hours and 
7 minutes, while in the present work it was determined that Olympia oysters remain 
open well over 20 hours daily. These differences are only proof that the oyster is 
sensitive to various factors in the environment, such as temperature, as shown above, 
AM P.M. 
Figure 10. — Records of two specimens of O. virginica, one in darkness (solid points) 
and one exposed (circles), in running water at Galveston, Tex., during 25 days. 
Shows percentage of time each specimen was open during each of the daily hours 
over this period 
and that the number of feeding hours daily depends upon how favorable all such 
conditions may be. 
In contrast to the results stated above are those obtained at Beaufort with pre- 
sumably normal oysters in running water which so far as known was not contami- 
nated. In the case of one specimen (fig. 7), tested for nearly two months in October 
and November, the average number of hours open daily was 14.45, which is quite low. 
However (fig. 8) the two specimens tested under like conditions in summer for 78 days 
were open an average of only 10.39 hours per day. The four specimens shown in 
Figure 9 were in still, artificially aerated water, and remained open an average of only 
6.57 hours daily. With the exception of the last mentioned, these specimens were 
apparently living under as favorable conditions as in the case of the tests with Olympia 
oysters. 
In the tests made at Galveston (fig. 10) the specimen in darkness averaged 17.5 
hours per day open, while the exposed oyster remained open an average of 19.4 hours 
