an oyster kept under the continuous pull of the 

 relatively light weight of 2 kg. (606 g./cm.^ of 

 cross section of muscle area) are shown in figure 

 164. The five lines represent excerpts of about 

 7.5 hours duration from a continuous recording 

 made at a temperature of 13.9° to 14.1° C. and 

 salinity of 31.3 °/oo- In line A the movements are 

 normal. Their amplitude is increased after the 

 application of a pulling force of 2 kg.; at the same 

 time the frequency of contraction decreases 

 (hne B). This condition continues until the 

 67th hour (line D, middle part) when the muscle 

 begins to stretch and the number of contractions 

 greatly increases. At the 71st hour (end of line 

 D) the muscle does not respond to stinmlation. 

 After removal of the weight (line E) shell move- 

 ments are restored. The frequency of contrac- 

 tions during the recovery period is greater than 

 under normal conditions. Within the next 48 

 hours normal shell movements of the type shown 

 in line A are resumed. 



Similar experiments in tlie air at higher tempera- 

 tures varying from 18.5° to 24.0° C gave slightly 

 different results shown in figure 165. The pulling 



Figure 164. — Shell movements of C. virginica in sea 

 water under continuous pull of 2 kg. (606 g./cm.^ of 

 cross-sectional area of the adductor muscle). Tempera- 

 ture 13.9° to 14.1° C. Salinity 31.3 °/oo- A— normal 

 shell movements before the application of weight. 

 R — immediately after the application of weight. 

 C — after 32 hours; note increased gaping. D — after 

 64 hours; wide gaping, complete loss of tonus and lack 

 of response to stimulation. Maximum valve opening 

 1.5 cm. E — increased muscular activity during the 



recovery period following the removal of the weight. 

 Time interval: A, B, C, D, and E, 0.5 hour each. 



WEIGHT OFF 



Fir.uRE 165. — Excerpts of the continuous records of shell 

 movements of C. vinjinica in air under the pulling force 

 of 2 kg. (500 of the cross-sectional area of the adductor) . 

 A — line ends at the y6th hour after the application of 

 force; B— at I90th hour; C— at 274th hour when the 

 muscle failed to respond to stimulation. Widest gap of 

 valves 1.5 cm. Temperature 1S.5° to 24° C. Time 

 interval: A, B, C, 0.4 hour each. 



force of 2 kg. per oyster applied in this case 

 was equivalent to 590 g./cm.^ of the cross-sectional 

 area of the muscle. Loss of tonus was attained in 

 this case after 274 hours (line C) when the gap 

 between the valves reached the maximum of 1.5 

 cm. Pathological condition of the muscle was 

 apparent after 96 hours (line A) and becam e pro- 

 nounced at 190 hours (line B). After removal of 

 the weights the oyster was left in running sea water 

 but failed to recover and died in 2 days. 



A lighter weight (315.5 g./cm.'^ of muscle area) 

 appUed to an adult oyster kept in running sea 

 water at temperatures ranging from 13.9° to 18.0° 

 C. produced very slow changes in the normal shell 

 movements (fig. 166). The upper line of figure 

 166 represents normal movements recorded imme- 

 diately after the application of the weight. A 

 noticeable increase in the amplitude of contractions 

 began on the 3rd day and continued tlirough the 

 11th and 12th days. During the 13th and 14th 

 days the amplitude of up and down strokes was 

 greatly reduced; loss of tonus and failure to re- 

 spond to stimulation developed by the 18th day. 

 Tlie last line sliows tlie typical staircase contrac- 

 tion following the removal of the weight, indicating 

 that the muscle retained some of its elasticity. At 

 the maxinmm ampHtude of the contractions (9th 

 and nth days) the oyster periodically lifted the 

 weight of 1 kg. to the lieight of about 1 cm. Ten 

 days after the end of tlie test the oyster recovered 

 completely and its shell movements became 

 normal. 



THE ADDUCTOR MUSCLE 



179 



