TEMPERATURE 81 



gradual increase in the rate of ciliary activity over the range to 

 35 °C, although above about 32°C the amplitude of beat was 

 found to be reduced. Further increase in temperature gave 

 further reduction in amplitude followed by a reduction in the 

 rate of beat of the cilia. Mytilus frontal cilia ceased to beat below 

 40°C, and at that temperature they were stationary in the relaxed 

 position, while further heating to 45 °C caused a change to the 

 contracted position. Up to this temperature the changes were 

 reversible, but at 47 °C an irreversible change took place and the 

 cytoplasm became opaque and coagulated. 



Similar changes have been reported in the activity of the 

 membranelles of Stentor (Sleigh, 1956a, b). The changes in 

 frequency of beat, metachronal wavelength and metachronal wave 

 velocity measured in an experiment on a row of these compound 

 cilia are shown in Table 5. It is seen here that the wavelength 

 changes with temperature, although not in a very regular manner. 

 Aiello (1960) has found a similar change in wavelength in Mytilus 

 cilia which was not detected by Gray (1930) or Lucas (1932b). 

 The maximum rate of beat of Stentor membranelles occurs at 

 about 30°C, above which the beat becomes intermittent and the 

 frequency falls away. The metachronal wave velocity shows 

 similar changes up to 36 to 38°C, at which temperature the 

 metachronal co-ordination finally breaks down; the cilia cease 

 beating below 40°C. 



Secondary effects of high temperatures are found in the activity 

 of both Mytilus and Stentor cilia at temperatures above 25 to 28 °C. 

 Below this temperature all changes of ciliary activity are rapidly 

 reversible, indeed, in experiments on the effect of temperature on 

 Stentor^ the frequency was found to change to the level appropriate 

 to its new temperature almost immediately (in a very few seconds 

 at the most), and would then remain constant at that temperature 

 for a long time. If the temperature was raised from say 20°C to 

 30°C and kept at the higher temperature, the frequency gradually 

 fell away; on return to 20°C, the frequency was found to be 

 below its original level and took some time to return to that level. 

 The higher the temperature, the more marked are the secondary 

 changes. 



The primary effect of temperature on ciliary frequency and 

 metachronal wave velocity may be compared by the application 



