only for a short time. Even when the valves 

 opened, the gills produced a weak and unsteady 

 current interrupted by frequent cessations of ciliary 

 motion. 



The effect of temperature on ciliary activity can 

 be seen more clearly in the experiments in which 

 only a single gill filament was used. The results 

 are shown in figure 135 in which the median fre- 

 quencies of the beat are plotted against the tem- 

 perature. As in previous observations 10 readings 

 were made at each temperature step and the entire 

 experiment was completed in about 2K hours. 

 The frequency of beat rapidly increased between 

 10° and 25° C. The slowing down of ciliary mo- 

 tion below 10° C. was gradual until all movements 

 ceased at about 6° C. The curve shown in figure 

 135 has four distinct slopes that indicate the dif- 

 ferences in the response of the lateral cilia to tem- 

 perature changes: a) a very slow increase between 

 6° and 11° C; b) a more rapid acceleration 

 between 11° and 15° C; c) a gradual increase be- 

 tween 15° and 25° to 26° C; and d) a decline as 

 the temperature rises toward the 30° C. mark. 



COMPOSITION OF SEA WATER AND 

 CILIARY MOTION 



Ciliary motion may be affected by changes in 

 the chemical composition of sea water and by 

 various drugs. Ionic balance t)f the outside me- 

 dium is one of the principal conditions for con- 

 tinuous ciliary activity of the gill. The most 

 important ions are sodium, potassium, calcium, 

 and magnesium; the increase in concentration of 

 one without a corresponding compensation in the 

 concentration of another or the withdrawal of one 

 of the ions may completely disrupt tlie ciliary 

 motion. 



EFFECTS OF CHEMICALS ON CILIARY 

 MOTION 



METALLIC IONS 



The most favored object for study of the effect 

 of ions on ciliary motion of bivalve gills lias been 

 the frontal cilia of the excised pieces of Mytilus 

 gills (Lillie, 1906; Gray, 1922b). Only occa- 

 sionally were tlie lateral cilia used in these obser- 

 vations. 



The monovalent metallic ions are important in 

 the stability of the ciliated colls and maintenance 

 of ciliary motion. By using a series of samples of 

 artificially varied sea water it can be shown ex- 

 perimentally that the replacement of sodium by 



10 15 20 



TEMPERATURE, 



Figure 135. — Effect of temperature on the median fre- 

 quencies of beat in number per second of the lateral 

 cilia of C virginica. Readings were made with Strobotac 

 on a single filament of the gill kept in sea water in a 

 microaquarium. Temperature was changed by circu- 

 lating warm or cold water in the jacket of the micro- 

 aquarium. Duration of the experiment lYi hours. 



other monovalent cations rapidly affects the rate 

 of ciliary beat. The effect is the greatest with 

 lithium and smallest with potassium. In the 

 order of their effectiveness the ions can be placed 

 as follows: Li< Na< NH3< K. There is, how- 

 ever, a marked difference between the effects 

 produced by sodium and potassium. The frontal 

 cilia beat more rapidly in solutions containing 

 greater concentrations of potassium and are less 

 affected by changes in the concentration of sodium. 

 The laterofrontal cilia of Mytilus are affected by 

 potassium in a manner not observed in other cilia. 

 The first reaction to the increased concentration 

 of this ion is an increase in the rate of beating. 

 With further addition of potassium the recovery 

 stroke becomes incomplete and the cilia vibrate 

 very rapidly with greatly reduced amplitude and 

 impaired efficiency. 



Magnesium inhibits the beat of the lateral cilia 

 of the excised pieces when the concentration of this 

 metal in the surrounding water exceeds its con- 

 centration in the blood. Potassium antagonizes 

 the action of magnesium while sodium produces no 

 such effect. 



Tlie difference between the effects of magnesium 

 and potassium is also apparent in tlie way these 



THE GILLS 



139 



