In the past 150 years, conceptions of the structure of the cytoplasm have undergone many revisions and refinements . A recent revision has been the introduction of the concept of the cytoskeleton. Although the modern era of this research field is only about a decade old, the roots of the cytoskeleton concept can be traced back to the early days of the cell theory . In fact , the very term “cytoskeleton” was introduced by JOHN T. NEEDHAM more than 200 years ago, but it was mainly used to describe exoskeletal structures of protozoans. Its use in conjunction with studies on endoskeletal, fibrillar components is much more recent (e.g., FRANZ 1939). In broad biological terms, the cytoskeleton can be thought of as the integrated system of molecules that provides cells with shape, internal spatial organization, motility, and possibly a means of communication with other cells and the environment. It is also the molecular basis of some of the physical properties of cells such as rigidity and elasticity. Dissection of this complex system has been essential for approaching it experimentally. One way of separating the cytoskeletal apparatus from other cell components is to solubilize less stable cell components in non-ionic detergents. Hence, the cytoskeleton can also be operationally defined as the material that remains after cells are treated with a detergent that removes membranes, organelles, small molecules, and soluble proteins. This cytoskeletal residue retains many of the structural and some of the functional properties of intact cells and is more accessible to a variety of experimental analyses. To-date, “the cytoskeleton” is essentially equated with “the cell residue after detergent extraction” .