EXPERIMENTAL STUDY OF THE OYSTER GILL 



2Z 



few minutes. The experiments show that at low temperature in a closed shell the 

 ciliary motion may be inhibited completely and that when the oyster is exposed to 

 direct sunlight the temperature of its meat becomes much higher than that of the 

 air. These facts should be taken into consideration when the hibernation of oysters 

 is regarded from the sanitary point of view. 



STRAINING OF WATER BY THE GILLS 



One of the main functions of the lamellibranchiate gUls consists in straining the 

 water that passes through its body and catching planktonic organisms and other 

 food particles suspended in it. It is interesting to study this function more care- 

 fully and to determine how completely the water is deprived of suspended material 

 after it had passed through the gills. This can be done easily by employing the 

 "tank" method. The oyster is placed in the tank (fig. 2) and is allowed to filter 

 water, which is collected in a graduate. After 1 liter has been collected the water is 

 passed through the high speed (Foerst's) centrifuge (making about 20,000 revolutions 

 per minute), the sediment is collected and transferred into a small volume of water, 

 and the number of organisms in it is counted in a Sedgwick-Raf ter cell. A comparison 

 of the number of organisms present in the water before and after it had passed through 

 the gills gives us a good idea of the efficiency of the latter as a filter. Obviously the 

 number of organisms that can pass through the gills depends on the size and shape 

 of the various forms. Long diatoms lilce Rhizosolenia or those that have long append- 

 ages, like Chsetoceras, are easily retained by the gills; while minute forms, and espe- 

 cially bacteria, have a good chance to pass between the lateral cilia. The first experi- 

 ments made in 1925 (Galtsoft", 1926) have shown that over 99 per cent of certain 

 plankton forms may be caught by the giUs. The plankton in these experiments 

 consisted of Chsetoceras, Rhizosolenia, and comparatively large dinoflagellates like 

 Peridinium oceanicum and Ceratium. Different results were obtained, however, 

 in the summer and autumn of 1926, when the plankton consisted chiefly of small 

 organisms. Following are the results of two experiments made in August and 



September, 1926: 



Table 8. — Filtering of water by the gills 



EXPERIMENT A, AUGUST 11, 1926. TEMPERATURE OF WATER 22°; RATE OF FLOW OF WATER THROUGH 



THE GILLS 1.01 LITERS PER HOUR 



EXPERIMENT B, SEPTEMBER 19, 192C. TEMPERATURE OF WATER 19.1°; RATE OF FLOW OF WATER 



THROUGH THE GILLS, 1.9 LITERS PER HOUR 



