Figure 414 from Chapter 16 (Cytoplasmic matrix and cytoskeleton) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. Transverse section of a portion of the cortex of a partially extended Stentor coerulus shows a cilium flanked by two microtubule arrays in cross section. The microtubules are interconnected by short bridges to form ribbons that are attached to basal bodies of neighboring cilia. During extension, the overlapping ribbons of stiff microtubules slide with respect to on another, decreasing their degree of overlap and causing the organism to elongate. Underlying myonemes contract to shorten the organism. From Huang and Pitelka, J. Cell Biol. 57:704-728, 1973 (PMID:4633444). A PDF copy of the accompanying chapter is available on the ASCB’s BioEDUCATE website.