F^ 



Figure 174. — Diagram of apparatus designed by Hopliins (1933, p. 474) to record relative rate of cloaeal current and 

 shell movements of oyster. S — lever for recording shell movements; s — fixed bar indicating on liymograph paper 

 closed position of valves; F — lever recording cloaeal current; f — fixed bar indicating zero position of F when no 

 current is present; F' — vertical rod bearing cone C against which the current strilces and turns it on axis A; balance 

 B; adjustable weight — W. 



lever B with an adjustable weight W. The cone 

 and current recording lever are fixed to a single 

 stand and so placed that the cone is directly in 

 the path of the cloaeal current. The lever S 

 records the movements of the upper valve of an 

 oyster immobilized in cement. The two fLxed 

 bars s and f shown at left are set in such a way 

 that they record continuously on the kymograph 

 paper the closed position of the shell (s) and the 

 zero position of current flow (f). The actual 

 amount of water transported by the gill cannot be 

 measm'ed by this method, but the relative values 

 corresponding to the rate of discharge are com- 

 puted by measuring with a planimeter the area of 

 the record enclosed between the lines made by the 

 excursions of the lever dm-ing a known time. A 

 sample of the record obtained by this method is 

 shown in figure 175. 



Records of changes in the velocity of the cloaeal 

 current obtained in this manner can not be ac- 

 curately calibrated. In my experience a cone 

 placed in front of the cloaeal current frequently 

 fails to come back to the zero position and the 

 entire delicate system easily gets out of adjust- 

 ment. Another weakness of the method is the 

 uncertainty of the correct position of the cone in 

 relation to the diameter of the stream; it is im- 

 possible to know whether the entire width of the 

 column of mo\-ing water strikes the cone surface. 



A method based on a similar principle was 

 developed by Mironov (1948) in the course of 

 studies of water filtration by Black Sea mussels. 

 The mollusk (M, figure 176) is placed on a hori- 

 zontal platform (P) mounted on the side of an 

 aquarium about 5 to 6 cm. below the surface of the 

 water. A cover slip (R) freely suspended by two 



Figure 175. — Relative rate of water transport by the gill of C. gigas obtained with Hopliins' method at 13.7° C. Repro- 

 duced in part from Hoplcins' paper, 1933. Portion of Ivymograph record shows: relative strength of cloaeal current 

 F; zero position of lever corresponding to absence of current f ; and 5-minute interval on record, two vertical lines T. 



TRANSPORT OF WATER BY THE GILLS AND RESPIRATION 



191 



