36 BTTLLETIN OF THE BUREAU OF FISHERIES 



current is running; /i>= viscosity of water in poises; and S= speed at the axis of the 

 tube in centimeters per second. 



3. The rate of flow of water produced by the gills is controlled by the temper- 

 ature. The optimum temperature lies between 25° and 30° C. No current is pro- 

 duced at 5° and below, although the cilia continue to beat. Absence of current at 

 low temperature is due to the lack of coordination of the ciliary motion along the 

 surface of the gill. 



4. Hibernating oysters do not exhibit any adaptation to low temperatm-e; 

 they begin to produce a current as soon as the temperature rises above the critical 

 point. In the majority of the oysters the current begins to flow when the tempera- 

 ture reaches 8° C. 



5. There exists considerable individual variation in the rate of flow of water 

 produced by different oysters. The ma.ximum rate of flow observed during the pres- 

 ent investigations is 3.9 Uters per hour at 25° C. 



6. The ciUary motion may continue at temperatures below 0° but becomes very 

 slow and irregular. There is a noticeable difl'erence in the efficiency of the frontal 

 and lateral ceUs; the first ones are able to transport the particles along the surface 

 of the gill at 3° C, while the lateral cifia can produce a current only above 5° C. 



7. In straining water through the gills the oyster catches a considerable number 

 of plankton organisms, but a certain per cent of them (from 1 to 18.9) escapes. The 

 number of organisms that passes through the giUs depends on their shape and size; 

 small, elongated forms, devoid of any appendages, pass easily between the lateral 

 cifia and escape. Bacteriological examination shows that from 50 to 89.2 per cent of 

 bacteria present in the sea water pass through the gills. 



8. The analysis of 132 daily records shows that the oyster has a tendency to keep 

 its shell open as long as possible. On the average, the shell of an oyster remains 

 open for 17 hours and 7 minutes during every 24-hour period. There is no correla- 

 tion between the opening and closing of the shell and the time of day. 



9. The results of the present investigation have many bearings on various prob- 

 lems of oyster industry, (a) They confirm the theory of hibernation and show that 

 at a temperature of 5° and below oysters cease to feed. (6) the knowledge of the rate 

 of filtration of water at various temperatures is essential for a successful application 

 of methods of self-purification, consisting either in relaying the oysters on unpolluted 

 bottoms or in purifying them with chlorinated water, (c) The knowledge of the rate 

 of filtration of water is of fundamental importance for a study of growth, fattening, 

 and ripening of the oyster. 



BIBLIOGRAPHY 

 Allen, William Ray. 



1914. The food and feeding habits of fresh-water mussels. Biological Bulletin, Marine 

 Biological Laboratory, Vol. XXVII, No. 3, pp. 127-146, 3 pis. Lancaster. 

 Committee on Sanitary Control of the Shellfish Industry in the United States. 



1925. Report. U. S. Pubhc Health Service, Public Health Report, Supplement No. 53, 17 

 pp. Washington. 

 Committee on Standard Methods for the Bacteriological Examination of Shellfish. 

 1922. Report. American Journal of Public Health, Vol. XII, July, 1922, No. 7, pp. 574-576. 

 Chicago. 

 Crozieb, W. J. 



1924. On the critical thermal increment for the locomotion of a diplopod. Journal of Gen- 

 eral Physiology, Vol. VII, No. 1, September 20, 1924, pp. 123-136, 7 figs. Baltimore. 



