of a small glass rod inserted in a hole drilled in the 

 supporting arm. It is convenient to have at hand 

 levers of various lengths so that records of shell 

 movements of sevei'al oj-sters can be made 

 simultaneously on one kymograph drum. Unless 

 there are some special reasons for not changing the 

 sea water during the observations, the oj'sters are 

 placed in running sea water, and the temperature 

 of the water is recorded on a thermograph and its 

 salinity checked at regular intervals. 



The records reproduced in this book were 

 obtained by using a slow-motion kjanograph. 

 The uppermost position of the writing pen always 

 corresponds in these tracings to the position of a 

 completely closed right valve; the lower position 

 of the line marks the various degrees of opening of 

 the shell. The magnitude of the up and down 

 excursions of the writing pen depends on the ratio 

 between the two arms of the lever, the distance 

 between the hinge ligament and the place of the 

 attachment of the string, and the height of the 

 oyster. The magnification of shell movements 

 recorded in the Bureau's shellfish laboratorj' at 

 Woods Hole varied from three to seven times the 

 actual excursions of the valves. A baseline 

 representing the position of the writing pen when 

 the shell is completely closed (not shown in the 

 records reproduced here) may be obtained by 

 rotating the drum rapidly before beginning 

 observations. 



Under ordinaiy circumstances the opening and 

 closing movements of the shell are so small that 

 the corresponding up and down tracings on kymo- 

 graph paper are relatively short and are not dis- 

 torted by the actual movement of the lever, which 

 on wider tracings describes an arc on the side of 

 the rotating cylinder. In case of wide gaping 

 produced by experimental stretching of the muscle 

 the distortion becomes serious since the writing 

 point at the bottom moves ahead of the time 

 marker and draws a gentle slope instead of a steep 

 curve. To avoid possible misinterpretation the 

 true position of the writing lever at the time of 

 maximum stretching and its return to the top as 

 the muscle contracts are shown on the records by 

 dotted lines. 



For long-term observations the speed of the 

 kjonograj)!! drum is adjusted to slow movement of 

 about 1 inch per hour, ^^^len studies are made 

 of the reactions of oysters to various stimuli the 

 speed of the rotation should be increased to about 

 three-eighths of an inch (1 cm.) per minute. With 



the fast- and slow-motion kymograph used in 

 the Bureau's shellfish laboratory, the latter speed 

 corresponded to one complete revolution of the 

 drum per hour. With this technique several 

 thousands of records of shell movements of oysters 

 were obtained under a great variety of conditions 

 using both normal and diseased oysters. Speci- 

 mens used in the tests were taken from New 

 England waters, Chesapeake Bay, South Carolina, 

 the west coast of Florida, Mississippi, Louisiana, 

 and Texas. A relatively small number of records 

 were made of shell movements of C. gigas and 

 0. lurida of the Pacific Coast. Many records 

 were obtained while oysters were subjected to 

 various types of poisons (chlorine, phenol, black 

 liciuor and red liquor of pulp mill wastes, crude oil, 

 thiocyanates, etc.) or while they were given 

 various concentrations of carbohydrates and 

 suspensions of pure culture of Escherichia coli. 



For a study of shell movements under normal 

 conditions the oysters were kept in running sea 

 water delivered at 10 times, at least, faster than 

 the rate at which it was transported through the 

 gills. Under this condition one can be certain 

 that the products of metabolism were removed and 

 the oj'Sters were not deprived of food. 



Shell movements play an essential part in the 

 respiration, feeding, and rejection of silt, mucus, 

 and excreta that otherwise may accumulate in 

 the pallial cavity of the oyster. Material settled 

 on the gills and mantle is rejected by rapid and 

 powerful snapping of the valves. In addition to 

 this rejection reaction there are smaller and 

 slower changes in the tonus level of the adductor 

 which may be interpreted as adjustments to a 

 steady flow of water through the gills. It is not 

 surprising that shell movements of oysters show 

 great variations both in the rate and type of 

 contraction. Analysis of the records made under 

 known conditions in the laboratory indicates 

 that in spite of this variability the movements of 

 individual oysters can be grouped into five major 

 types characterized bj^ their responses to various 

 conditions. 



FIVE MAJOR TYPES OT SHELL 

 MOVEMENTS 



In comparing the records of shell movements it 

 is necessary to know the followang essential points: 

 the highest and lowest level reached by the 

 writing pen during the periods of closing and 

 opening of the valves, the frequency at which 



THE ADDUCTOR MUSCLE 



169 



