[Evolutionary transformations of the esophageal lining in vertebrates and man in light of the theory of phylembryogenesis].

The comparative histological study of processes of embryonic histogenesis of the oesophagus epithelium in certain representatives of vertebrate animals (fishes, amphibia, reptiles, birds, mammals) and man was carried out in the light of the academician A. N. Severtsov's theory of phylembryogenesis. It has been shown that phylogenetic changes of the oesophagus lining of vertebrates related with its evolutionary transformations are regularly reflected in the stages or steps of the oesophagus epithelium histogenesis in ontogenesis of each systematic unit of the subtype. The first step is the phylembryogenesis of the oesophagus lining in all vertebrates is the monolayer epithelium of the endodermal origin; the secone step is the striated muco-ciliated (in low vertebrates and most reptiles) and pseudostratified (embryos of higher vertebrates) epithelium; the third step is the pseudostratified mucous epithelium (bony fishes) and stratified lining (prefetuses of higher vertebrates). The forth step is the stratified mucous (steppe turtle) and stratified muco-ciliated epithelium (fetuses of birds, many mammals and man). The fifth step--stratified squamous epithelium (birds, mammals, man). The academician A. N. Severtsov's theory of phylembryogenesis clearly points to the origins (the entoderm), routs and mechanisms of the transformation of the oesophagus lining in its evolutionary development.