Two significant features of the origin and development of kinetosomes in the ciliate, Oxytricha fallax, are indicated by electron micrography of serial sections. (1) Some kinetosomes arise in varied orientations to adjacent kinetosomes instead of in the single orientation regularly found in other material; and some kinetosomes arise in positions that are not adjacent to any kinetosome. Hence, even in ciliates, some kinetosomes arise without using existing kinetosomes or their micromilieu as nucleation sites. (2) Growth of kinetosomal microtubules appears to occur at their proximal as well as distal ends. This is indicated by proximal cross-sections with only one or two microtubules of a triplet, while more distal sections of the same incompletely grown kinetosome show the complete triplet pattern.

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