The unexpected results from an investigation into hereditary congenital anorectal malformations of pig embryos have demonstrated the weakness of earlier interpretations and constructions and underlined the need for a new inquiry into the normal development of the area in human embryos. It demonstrated that although data from malformations may offer extra information about the normal development of the area, great care has to be taken in using that information for the reconstruction of its normal development which should be firmly based on the observation of the evolving microscopic anatomy of...