 As we have seen, model organisms have greatly shaped the development of experimental biology, and continue to do so. Another important entity are so-called experimental systems. These are not to be confused with model organisms: The latter is a biological species that is being bred in the laboratory for experimental work. An experimental system may involve one or several model organisms, and most model organisms are used in several experimental system. An experimental system typically consists of certain research materials (which may be obtained from a model organism), preparatory procedures, measurement instruments, and data analysis procedures that are mutually adapted to each other.