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Figure 191. — Shell movements (upper line) and oxygen 

 uptake (vertical bars) of an adult C. virginica before and 

 during the application of a pulling force of 4 kg. Sharp 

 inflection of the curve at about .3^4 hours corresponds to 

 the point of tearing off the muscle. July experiment. 

 Temperature 23.7° C. 



their surface is not in direct contact with sea water. 

 The high oxygen uptake after they are shed into 

 the water is probably due to the greatly increased 

 free surface areas of these cells. 



In these observations the forcible stretching of 

 the adductor muscle was always associated with 

 a decrease and eventual cessation of ciliary current. 

 Under the conditions of the tests the velocity of 

 the cloacal current could not be measured, but 

 decrease in current velocity was observed by the 

 movements of particles suspended in the water or 

 by the slanted position of the fecal ribbons, which 

 in actively feeding oysters are horizontal to the 

 axis of the cloacal current. 



Two inferences can be deduced from these obser- 

 vations: First, the uptake of oxygen is dependent 

 primarily upon the rate of water transport by the 

 gills; and second, in maintaining a tonus level the 

 locking meclianism of the adductor muscle is not 

 dependent on the uptake of oxygen from surround- 

 ing water. 



These observed rates of oxygen uptake are 

 considerably greater than those found by J0rgensen 



2 KILOGRAMS 



5 6 



Figure 192. — Shell movements and oxygen uptake of an 

 adult C. virginica before and after the application of a 

 pulling force of 2 kg. Oxygen uptake in mg. per oyster 

 per hour is shown by vertical columns. July. Tem- 

 perature 22.4° C. 



(1952) for adult C. virginica of Woods Hole. The 

 oysters used in his experiments were supplied from 

 the Bureau's shellfish laboratory and were ap- 

 proximately of the same size as those which I 

 tested in the preceding summers. The rate of 

 o.xygen uptake determined by J0rgensen was less 

 than 1 ml. per hour (1.5 mg. of o.xygen per oyster). 



UI 



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UJ 

 Q. 



CC 



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HOURS 



2.5 3.0 



Figure 193. — Oxygen uptake of an adult oyster under 

 normal conditions and after the application of a pulling 

 force of 2 kg. Sudden increase of o.xygen consumption 

 at 254 hours is due to the discharged sperm. Upper line 

 indicates shell movement. July. Temperature 24.8° C. 



210 



FISH AND WILDLIFE SERVICE 



