EXPERIMENTAL STUDY OP THE OYSTER GILL (l§ 



flow of water through the gills. His method is open to several objections. Fu-st, 

 because of the seasonal and daily fluctuations in the abundance of diatoms in water 

 the average figure may differ greatly from the diatom content at the time of obser- 

 vation. Second, not all of the diatoms strained by the gills are ingested; certain 

 numbers of them may be rejected into the pallial cavity and do not reach the diges- 

 tive tract. 



Virtually the same method as that employed by Grave was used by Moore (1913) 

 in studj'ing the oysters of Mississippi. Nelson (1921), studying the feeding of oysters 

 in Barnegat Bay, adopted the following procedure: At ebb tide oysters were placed 

 on a platform built in the bay; when the tide began to run the investigator watched 

 for the opening of the shells and kept them continuously under observation for one 

 hour. Meanwhile, every two minutes a sample of the water that was passsing over 

 the oysters was taken and the number of Tintinnopsis (a protozoan, which wa.s taken 

 as an index) was counted. At the close of the hour two oysters were opened, the 

 stomachs washed out, and the contents counted. The number of Tintinnopsis 

 collected by the two oysters compared with the number in the water gave the rate of 

 current produced by the oyster. Nelson assumes that the stomachs of the oysters 

 he examined were empty because, according to his observations, when an oyster 

 opens after a period of closure of one hour or more its stomach is virtually empty of 

 food. . ' I 



An entirely different method was employed by Viallanes (1892) and ttarison 

 (1926) in experiments on European oysters and mussels. Their method is based on 

 the determination of the amount of clay precipitated by the mollusks during a period 

 of 24 hours. The mollusks are kept in the crystallizing dishes placed on the bottom 

 of a tank filled with water, to which a known quantity of clay (0.05-16 gi-am per liter) 

 is added. Several dishes are placed in the same tank for control without the animals. 

 After 24 hours the sediment that has accumulated on the bottoms of the dishes is 

 collected, dried, and weighed. The figures thus obtained are corrected by sub- 

 traction of the amount of precipitate by gravity (in the controls), and the rate of 

 filtering of water through the gills is thus computed. These authors used their method 

 chiefly for the determination of the relative filtering ability of European and Portu- 

 guese oysters. They fail, however, to give a record of the temperatm'e of the water 

 and do not state whether the shells of the mollusks were open all the time during the 

 experiment. The possible source of error in this method lies in the fact that the 

 mucus discharged by the gills may cause the agglutination and precipitation of the 

 clay, and therefore the amount of precipitate on the bottom is not a safe measure of 

 the activity of the gills. 



ilv In a series of papers Piitter (1909, 1911, 1924) has estimated the rate of flow of 

 water by measuring the CO3 production and O2 consumption by various marine 

 organisms. As a result of this study he arrived at the conclusion that in order to 

 receive a required amount of carbon from plankton the organisms in question should 

 filter tremendous volumes of water. Thinking that this is impossible he advanced 

 the hypothesis, which was much criticized by other investigators (Moore, Edie, 

 Whitley, and Dakin, 1912), that the marine organisms feed by absolution of organic 

 matter dissolved in sea water. 



