The cytoskeleton can also be referred to as cytomusculature, because it is directly involved in movements such as crawling of cells on a substratum, muscle contraction and the many changes in the shape of a developing vertebrate embryo; it also provides the machinery for the cyclosis in cytoplasm. Cytoskeleton is apparently absent from bacteria and it may have been a significant factor in the evolution of eukaryotic cells. The cytoskeleton extends throughout the cytoplasm and is a complex network of three types of protein filaments, microtubules, microfilaments (actin filaments) and intermediate filaments (IFs).