Anaplastic cells display marked pleomorphism (variability). It derives its name from the architectural Pleomorphism (variable appearance) seen by light microscopy. One factor that affects the pleomorphism of some bacteria is their nutrition. These demonstrate various degrees of cytologic atypia, including hyperchromasia, pleomorphism, prominent nucleoli. The malignant cells are uniform and lack nuclear pleomorphism. Contamination is common due to their small physical size, lack of cell wall, and pleomorphism. Sergei Winogradsky took a middle-ground stance in the pleomorphism controversy. Mitotic activity is only moderate and pleomorphism is usually absent. Despite the prevalence of pleomorphism in human pathology, its role in disease progression is unclear. Nuclear pleomorphism is usually minimal and mitoses are infrequently seen. Pleomorphism is a synonym of polymorphism. Pleomorphism in "Mycoplasma" species allows bypassing of typical membrane filtration systems. A group of haloarchaeal viruses has been shown to exhibit pleomorphism as well. Nuclear pleomorphism is usually easily to identify, with the nuclei containing prominent nucleoli. In epithelial tissues, pleomorphism in cellular size can induce packing defects and disperse aberrant cells.