woter transport 



shell movement 



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water transport 



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shell movement 



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water transport 



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Figure 180. — Tracings of the rate of water transport and 

 shell movements of three adult oysters, C. virginica at 

 Woods Hole. Temperature 20° to 22° C. July. Ver- 

 tical strokes of water transport hne correspond to the 

 discharge of 247 ml. of water by the dumping vessel. 

 Time interval, 1 hour. 



full velocity and the opening of the valves were 

 about equal (fig. 181). 



A reduction in the rate of water transport may 

 also be caused by the slowing down of the lateral 

 cilia of the gill filaments. To studythe activity 

 of these cilia it is necessary to eliminate the 

 effects caused by the movements of the shell and 

 mantle. A record of the activity ol the lateral 

 cilia can be obtained with an electric drop counter 

 placed under the small tank (fig. 168) to receive 

 water discharged through the cloaca. Parts of 

 such a record made in the summer at Woods Hole 

 are reproduced in figure 173. Interruption of a 

 steady state shown on the second pair of lines in 

 figure 173 was caused by slight tapping against the 

 side of the experimental tank. The lateral cilia 



are very sensitive to minor mechanical stimuli 

 and slow down at the slightest disturbance. These 

 interruptions were of brief duration, and the 

 preceding rate was restored within a few seconds 

 (line three). 



By using the drop counting technique it is 

 possible to observe minor fluctuations in the ac- 

 tivity of the lateral cilia and to demonstrate their 

 responses to changes in temperature, salinity, 

 different concentrations of drugs, food particles, 

 etc. In a graphic summary of one such record 

 (fig. 182) the average number of drops per 5 sec. 

 was plotted against time shown at 5-sec. intervals. 

 The rate of current remained fairly constant with 

 the exception of the period between 110th and 

 145th sec. when a suspension of eggs was added 

 to the gills. The reduction was temporary, and 

 the normal rate was soon resumed. 



The dilation and constriction of the ostia and 

 the expansion and folding of the gill lamellae also 

 affect the rate of water transport. The effect of 

 these minor adjustments can not be measured 

 separately from the activity of the lateral cilia. 

 I have noticed, however, that changes in the 

 position of the gill lamellae and the expansion or 

 constriction of the ostia are usually associated 

 with the muscular activities of the adductor 

 muscle and the mantle. 



DISSOLVED ORGANIC SUBSTANCES AND 

 RATE OF WATER TRANSPORT 



Collier and his associates (1050, 1953) reported 

 that sea water of the Gulf of Mexico contains cer- 

 tain organic substances which have the general 

 chemical cliracteristics of carbohydrates. These 

 substances respond to analytical tests with 

 N-ethyl-carbazole (or with anthrone, Lewis and 

 Rakestraw, 1955) and were reported to occur in 

 concentrations up to 50 mg./l. The figm-e greatly 

 exceeds the concentrations found in sea water 

 by others. According to the reliable studies of 

 Krough (1934) the content of dissolved organic 

 matter in sea water remains fairly constant at the 

 level of about 5 mg./l. It was further claimed 

 by Collier that the carbohydrates occur in variable 

 concentrations in coastal water near Pensacola, 

 Fla., and that their presence greatly influences the 

 shell movements and the rate of water transport 

 by C. virginica. Since in their experiments the 

 response of the oysters was not consistent with the 

 concentrations of carbohydrates determined by 

 carbazole reagent, the authors tried to overcome 



TRANSPORT OF WATER BY THE GILLS AND RESPIRATION 



197 



