Eukaryotes: The Cilium

Abstract

The last cellular structure to which it is mandatory to dedicate a whole chapter is the cilium. It is a tiny swinging protrusion, typically a few micrometers long, but reaching sometimes a few millimeters, which swings at a variable frequency that does not usually exceed 40 cycles per second. Its image under the light microscope renders it trivial, while under the electron microscope an engineering brilliance is revealed, with ordered tubes kept together by proper connectors, sheaths and rack-motors. Its geometry is so surprising and enigmatic that it almost inhibits discussion on its origin. Only a few authors, at the risk of their reputation, have put forward their proposals, which turned out to be the most diverse.