Most current models for morphogenesis of repeated patterns, such as vertebrate somites,
cannot explain the observed degree of constancy for the number of somites in individuals of
a given species. This precision requires a mechanism whereby the lengths of someites (ie
number of cells per somite) must adjust to the overall size of individual embryos, and one
which co-ordinates numbers of somites with position in the whole pattern of body parts. A
qualitative model is presented that does admit the observed precision. It is also compatible …