2 
BULLETIN- OP THE BUREAU OP FISHERIES 
probably applicable to the eastern oyster ( 0 . virginica ) also, is suggested by tbe simi- 
larity between the behavior of this species (recorded without continuous thermograph 
records) and that of the Olympia oyster. 
METHOD 
The method of recording shell movements with the kymograph was similar to 
that of Galtsoff (1928). The specimens were set on a plaster of Paris base and im- 
mersed in an aquarium of about 3 liters capacity. Two specimens were in each 
aquarium. Freshly pumped sea water was running constantly. The recording levers 
were of celluloid strips, and the weight of the end carried by each oyster was so counter- 
balanced that there was no noticeable effect on the specimen. A long paper kymo- 
graph carrying a paper about 2 meters long was employed. 
The bulb of the thermograph was immersed in the water of the aquarium close 
to the oysters. The large size of the bulb was the source of a certain amount of error 
in the method. It extended from end to end of the aquarium, and while inflowing 
water of a changed temperature might strike a specimen and produce a reaction, it 
would be some time before the temperature throughout the chamber would be differ- 
ent enough to show a change on the record. The temperature chart showed what 
amounted to an average temperature in the aquarium, and for this reason would be 
relatively sluggish. In spite of this inaccuracy, however, the results are clear. 
EXPERIMENTS WITH OLYMPIA OYSTERS ( OSTREA LURIDA) 
NUMBER OF HOURS OPEN PER DAY 
Nelson (1921) found that oysters remained open an average of 20 hours per day, 
while Galtsoff (1928) obtained an average of 17 hours and 7 minutes. Such a dis- 
crepancy is probably due to environmental factors. Galtsoff noted that one specimen 
remained tightly closed for 67 hours while the temperature was between 0.5° and 
1.6° C. If temperature has a marked influence on shell movement, the difference 
between the results of Galtsoff and Nelson becomes clear. 
In Table 1, the data obtained with 18 specimens of Ostrea lurida are presented. 
During most of the tests the temperature was between 14° and 17° C., and these 
oysters were open a large part of the time. All results together show that, in spite of 
marked temperature fluctuations in certain cases, the oysters were open an average of 
20.45 hours per day. Eliminating those series in which the temperature was very 
changeable, and one series in which the water was contaminated for a while, the re- 
maining 12 specimens were open an average of 21.9 hours daily. Even when all of 
the results are considered the oysters were open and presumably feeding over 20 hours 
per day in spite of unfavorable conditions in certain cases. 
In the following section the unfavorable temperature conditions in the above cases 
are discussed. 
