Origin of vascular channels from epithelial tissue as shown in livers.
D000818:Animals; D001808:Blood Vessels / Q000196:embryology* / Q000254:growth & development*; D002642:Chick Embryo; D002645:Chickens; D006651:Histocytochemistry; D008099:Liver / Q000098:blood supply*; D009024:Morphogenesis