Cross section the 9 + 2 axoneme of the cilium of Tetrahymena. The plasma membrane covers the axoneme and is continuous with the plasma membrane covering the cell body. Each doublet tilts inward to the tangent of the axonemal cylinder. Two arms, an inner arm and outer arm, extend from the complete microtubule of each doublet. These arms have ATPase activity and are called dyneins. They cause one doublet to slide against the adjacent doublet. Other protein links in the axoneme are elastic and induce the characteristic bending of the cilium and prevent excess sliding as the doublets slide past each other. TEM taken on 7/15/67 by R. Allen with Philips 200 operating at 60kV. Neg. 19,200X. Bar = 0.2µm. The negative was printed to paper and the image was scanned to Photoshop. This digitized image is available for qualitative analysis. An unprocessed, high resolution version of this image (CIL:34601) is in the library and available for quantitative analysis. Additional information available at (http://www5.pbrc.hawaii.edu/allen/).