each test was from 16.6 to 20.5 beats per second. 

 The greatest difference ])etween the individual 

 oysters was recorded in two lipe males; one had the 

 median frequency of 15.5 per second (at 23.3° C.) 

 while in the other the ciha beat at the rate of 24.8 

 per second (at 25.1° C). In the majority of the 

 oj^sters the median rate of ciha beat varied between 

 18 and 22 per second. 



Table 14. — Frequency of heat of lateral cilia of 14 adult 



C. virginica recorded at nearly constant temperatures 



[Readings were made at intervals of 1 or 2 minutes] 



Oyster 



Spawned out, sex un 



determined 



Two-year-old 



Ripe male 



Spawned out male.-. 

 Spawned out male. . . 



Ripe male 



Spawned out female. 

 Spawned out female 

 Spawned out female. 



Ripe female 



Ripe female 



Spawned out female. 

 Spawned out female 

 Spawned out female 



Record- 

 ings 



20 

 10 

 15 

 10 

 10 

 10 

 15 

 15 

 10 

 1(1 

 20 

 10 

 10 

 15 



EFFECT OF TEMPERATURE 



In evaluating- the biolooical sionificance of the 

 experimental data of the effect of temperature on 

 beat frequencies, one should remember that the 

 pieces of isolated tissue used were in an abnormal 

 situation. They were deprived of blood supply, 

 separated from close association with other struc- 

 tural elements of the gill, and subjected to in- 

 creased concentrations of metabolites. It is con- 

 ceivable that under normal conditions the lateral 

 cilia of an intact gill may react somewhat 

 differently. 



Stroboscope observations fully confirm the fact 

 that temperature controls the ciliary beat. This 

 effect was observed in a series of determinations 

 made during the summer using small pieces of 

 filaments taken from .39 adult New England 

 oysters kept in water at various temperatures. 

 At the start of each series of readings 10 minutes 

 were allowed for adjustment to the desired tem- 

 peratm-e which was kept constant within plus or 

 minus 1 ° C. Ten stroboscope readings were made 

 at 1-minute intervals and repeated at higher or 

 lower temperature. Xo more than three different 

 temperature levels were used on one preparation. 

 Careful precautions were taken to prevent the 

 movement of the e.xcised filaments in the micro- 



aquarium so that all the readings would be made 

 on exactly the same locus of the ciliary tract. 

 This was necessary because of the considerable 

 differences in the rate of beating which occasionally 

 occur along the adjacent filaments. 



The results, summarized in talile 15, show the 

 maximum median frequency' of 27.7 beats per 

 second at temperatures of 25° to 27° C. The 

 ciliary activity became irregular at about 35° C, 

 and the movement ceased at 37° to 38° C. 

 Wliether these limits are applicable to oysters 

 from warm southern waters is not known, since 

 all the obser\'ations were made only on the New 

 England oysters. Between 35° and 37° C. the 

 motion was so irregular that its frequency could 

 not be recorded with certainty. Irregular beating 

 at the rate of about two beats per second was ob- 

 served in some specimens during short exposure 

 til tlie temperature of 45.6° C. Judging by the 

 median values of the beat frequencies, the opti- 

 mum temperature is between 23° and 27° C. (see 

 fourth column, table 15). The ciliary activity 

 tleclines rapiiUy below 21° C. and ceases com- 

 pletely at 5° to 7° C. 



Individual variations in the frequency of beat 

 among oysters of a single population suggest dif- 

 ferences in their physiological states and different 

 reqiurements for food and water for respiration. 

 As a rule, spawned-out females remained inactive 

 for some time in late August ami early September. 

 During this period the gonads containing un- 

 spawned sex cells were reabsorbed and tissues be- 

 came watery because of the reduction in solids 

 content. The adductor muscles remained con- 

 tracted, and the shells were closed for unusuallj' 

 long periods, lasting from 3 to 4 days, or opened 



T.^BLE 1.5. — Frequencies of heal of lateral cilia of the gills of 

 adult C virginica at different temperatures 



[Stroboscope readings made on excised filaments kept in sea water] 



138 



FISH AXD WILDLIFE SERVICE 



