34 



BULLETIN OF THE BUREAU OF FISHERIES 



The only inference that can be drawn from an examination of this table is that 

 there is no correlation between the closures of the shell and darlaiess. Out of 103 

 days there were only 7 during which the oysters were closed only at night. There 

 were 43 days when the closures occurred during the daytime, and in 53 cases it took 

 place both during day and night hours. The number of hours of night closure is 

 266, or 32 per cent of the total number of hours of inactivity (831). Inasmuch a3 

 the period of darkness is approximately 8 hours, or one-third of the 24-hour p.-ri • 

 it is quite natural that one-third of the time of inactivity should fall in the night hours. 

 Examination of these records forces us to come to the conclusion that under labora- 

 tory conditions the periods of opening and closing of the shell of tlie oyster are not 

 correlated with time of day or night. 



There arises the question as to whether the temperature has any effect on opening 

 and closing of the shells. In the above-mentioned experiments the temperature 

 of the water varied from 13° to 22° C. Within these limits thei'e was no visible effect 

 of temperature on opening or closing of the shell. In February, 1927, eight records 

 were obtained on two oysters kept at temperatures varymg from 4.5° to 5.5°. The 

 results of this experiment are presented in the following table: 



Table 11. — Opening of shells at low temperatures 



The shells were open very slightly, less than 1 millimeter apart (fig.l2), but the 

 oysters exhibited typical periodical contractions. As has been shown above, no cur- 

 rent is produced at this temperature, and several tests with carmine suspension 

 failed to disclose any current in the oysters attached to the recorduig apparatus. 

 On February 15 one oyster was attached to the kymograph and left 67 hours in cold 

 water; during this time the temperature varied from 0.5° to 1.6° and the oyster 

 remained tightly closed. 



DISCUSSION AND CONCLUSIONS 



The experimental data presented in this paper show that the functioning of the 

 gills of the oyster is controlled by temperature. In spite of wide individual variations 

 in the activity of the cihary epithehum, it has been found that in all cases the ciliary 

 motion follows strictly the changes in temperature, slowing down with its fall and 

 increasing with its rise. Because of anatomical peculiarities, the normal functioning 

 of the gills ceases at a temperature of 5° C, when the ciUary motion becomes irregu- 

 lar and is not able to maintain the head pressure necessary for the production of an 

 outgoing current. The inhibiting effect of low temperature upon the activity of the 

 oyster was suspected many years ago. Basliford Dean (1887) was the first to suggest 

 that "in winter the oyster, with decreased movements of branchial ciha and reduced 



