The Form of Beat in Cilia of Stentor and Opalina

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Abstract
1. The patterns of beat in cilia of Stentor and Opalina are described. A fibrillar contraction mechanism is suggested to explain the beating of these cilia and of flagella. The diverse forms of beat are thought to result from differences in the relative timing of parts of the contraction process in different organelles. 2. In both types of ciliary beat the effective and recovery phases are in progress simultaneously and are inseparable parts of one continuous contraction process. 3. The average rate of propagation of the contraction wave in Stentor cilia was 844 µ/sec., which is comparable with the rate found in echinoderm sperm tails. In Opalina cilia the rate was much slower at between 20 and 100 µ/sec. 4. The peristomial cilia of Stentor always beat in the same direction, but Opalina cilia may show co-ordinated beat in any direction, and the form of beat appears the same whatever the direction of beat.