I. Flagella and cell bodies of Crithidia (Strigomonas) oncopelti were irradiated at preselected points with a pulsed ruby laser microbeam. Results were recorded by high-speed cinephotomicrography. A flagellum could be completely amputated at the irradiated point.

2. The portion of the flagellum between the cell body and the irradiated point beat from the base after irradiation. The amputated portion of the flagellum could beat from either the tip or the irradiated point, and could beat first from the tip and then from the irradiated point or vice versa. Beating could continue for up to ten cycles.

3. For flagellar activity in this organism neither a unique region of the flagellum nor the cell body is necessary. Wave propagation appears to involve the transmission of a signal at a greater velocity than that of the wave. The results favour a model of bend propagation which allows for a distribution of autonomous initiators along the flagellar length.

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