was warmed to the extreme high and cooled again 

 to 20° C. for the hist observation. Each circle 

 represents a mean of 10 consecutive readings made 

 at intervals of 2 to 3 minutes. The lower curve 

 represents the activity of an oyster in whicli slow 

 ciliary motion started only at 11.3° C. The upper 

 curve is typical for an oj^ster which maintains a 

 rapid transport of water. In both curves the 

 maximum activity occurred at 20° to 25° C. 

 Rapid acceleration in the rate of current took 

 place between 10° (or 11.3°) and 15° C. Essen- 

 tially the relationship between the temperature 

 and current velocity is similar to tiie effect of 

 temperature on the frequency of beat of lateral 

 cilia shown in figure 135, although the slope of the 

 latter curve is steeper than in the two curves 

 shown in figure 140. Within the range of the 

 temperature used in these tests, the action of tlie 

 cilia was completely reversible. 



The increased rate of activity induced by 

 temperature may be expressed by temperature 

 coefficients determined at 10° intervals. Tliese 

 values, calculated from a large number of obser- 

 vations with the cone method and given in table 

 16, show considerable difference in Qio based on 

 the determinations of current velocity and on the 

 rate of work. 



T.\BLE 16. — Temperature of coefficients {Qio), of the rale of 

 ciliary activity of lateral cells of C. virginica 



The current velocity is not a true measure of 

 the work performed by cilia because the viscosity 

 of the water changes with temperature. In the 

 formula W=2ttIiiS'^ the work required to maintain 

 a current at a constant speed is proportional to 

 viscosity, ;u. Since at a lovverte mperature the 

 viscosity of sea water is greater than at higher 

 temperatures, more energy is required to propel 

 cold water. As the work needed to pr(jduce 

 current of a given velocity is proportional to the 

 square of the velocity at the axis of the current, 

 it is apparent that the decrease in the frictional 

 resistance due to lesser viscosity of water is not 

 sufficient to compensate for the additional energy 



required for maintaining faster current. Tem- 

 perature coefficients computed on the basis of the 

 rate of work performed are, therefore, more 

 significant than the Qio based on the velocity of 

 current. 



HYDROSTATIC PRESSURE INSIDE 

 THE GILLS 



The velocity of the cloacal current is propor- 

 tional to tlie difference in hydrostatic pressure 

 inside the gill chambers and at the opening of the 

 cloaca. The pressure can be measured by in- 

 troducing an L-shaped glass tubing into the free 

 end of the rubber tubing inserted into the cloaca 

 and recording the difference between the level of 

 sea water in the tube and the level in the container 

 in which the oyster is kept. Correction should 

 be made for the position of the meniscus in the 

 tube due to surface tension. Using this simple 

 device I found that in an actively feeding adult 

 C vir(jinica the pressure inside the epibranchial 

 chamber may be as high as 7 to 8 mm. of sea- 

 water column. If the temperature and salinity 

 of water are known, the pressure may be calculated 

 in grams per unit area. 



SPONTANEOUS INHIBITION OF 

 CILIARY MOTION 



When tiie bivalve mollusks close their sliells 

 and cut off their access to outside water, they enter 

 a state of suspended animation during wiiich their 

 normal functions are greatly slowed down or 

 completely cease. This state of diminished ac- 

 tivity observed in Anodonta and Sphaenum 

 {Cydas) was regarded by Gartkiewicz (1926) as 

 sleep. Through the transparent shell of Sphacr- 

 i)i)7i he was able to see that the ciliary motion of 

 the gills and the beating of the heart were at a 

 complete standstill when the shells were closed. 

 This observation corrected the erroneous opinion 

 of earlier investigators (Wallengren, 1905a, 1905b) 

 that ciliary activity persists when the valves are 

 closed. 



The cessation of ciliary motion after tiie closing 

 of shells was attributed to the accumulation of 

 carbon dioxide and the decrease of pH. A pH 

 of less than 6.0 probably does not occur in the 

 body fluids of bivalves after they close tlieir 

 valves because of the buffering action of carbonates 

 of the shell substance. 



In the gills of C. lirginica ciliary motion ceases 

 shortly after the closing of the valves and is re- 



146 



FISH AND WILDLIFE SERVICE 



