In "Materials" Bateson noted and named homeotic mutations, in which an expected body-part has been replaced by another. The animal mutations he studied included bees with legs instead of antennae; crayfish with extra oviducts; and in humans, polydactyly, extra ribs, and males with extra nipples. These mutations are in the homeobox genes which control the pattern of body formation during early embryonic development of animals. The 1995 Nobel Prize for Physiology or Medicine was awarded for work on these genes. They are thought to be especially important to the basic development of all animals. These genes have a crucial function in many, and perhaps all, animals.