Microtubules from the Cilia of Tetrahymena Pyriformis

Frayed cilia from Tetrahymena pyriformis have been examined in the electron microscope using both uranyl acetate and phosphotungstic acid as negative stains. Observations on the central microtubules show that one member of the pair exhibits two rows of short projections. These are about 18 nm long, and are spaced longitudinally at 16-nm intervals. In many specimens the projections are separated from the tubule wall and appear as a ladder-like structure linked by one or more longitudinal filaments. These results are related to some recent work on sectioned material; it is likely that the projections are independent of any central sheath holding the two tubules together.