1. A stroboscopic method was used to determine the frequency of beat of the peristomial cilia of Stentor polymorphus (Ehrbg.). The metachronal wave-length was measured from photographs. These two values were used to calculate the rate of propagation of the metachronal wave.

2. The Arrhenius temperature characteristics for frequency and for wave velocity were calculated for the temperature range from o to 25° C. The average values found, 11,350 and 7520, were significantly different for the two factors.

3. An increase in the viscosity of the medium by addition of methyl cellulose caused a decrease in frequency, but no significant change in wave velocity.

4. The presence of magnesium chloride in low concentrations caused an increase in frequency, but no significant change in wave velocity. Aluminium chloride caused similar increases in frequency at lower concentrations than magnesium chloride.

5. The drug digitoxin had different quantitative and qualitative effects on the frequency and on the wave velocity. Small increases in frequency occurred over the concentration range in which large increases in wave velocity were recorded. The wave velocity increase reached a maximum at about 0.4 mg./l. of digitoxin and was some six times as great as the frequency increase at this concentration.

6. It is concluded that the mechanical process involved in ciliary activity functions independently of the co-ordination process. A combination of these two factors determines the magnitude of the metachronal wave-length.

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