A series of 17 human specimens including different ages of embryos,fetuses and adults were selected for the study of developmental changes ofthe digestive epithelium ranging from the esophagus to the large intestine.Each embryo was sectioned in series and stained with H.E.,while the partsof the digestive tract of the fetus and adult were obtained segmentally andstained with H.E.,I.H.,as well as Mallory's triple staining method.Com-plete sets of sheep and pig embryo were also utilized in comparison with theearly stage of human embryo.It was found that the development of the mucous folds,villi and glands,the morphological changes of the epithelium and the differentiation of thecytoarchitecture of the epithelial cells consecutively started from the fetalmonth.Consequently,the morphological constitution of the epithelial cells ofthe digestive tract of the adult was found to be specifically differentiatedfrom that of the embryonic condition.A great variation of the differentiation of the esophageal epithelium wasobserved during the fetal period.Patches of the different kinds of epithe-lium were intermingled in the same section of the prepared slides.The oc-curence of the various kinds of epithelium is considered as an instability ofthe life span,and the typical form of the stratified squamous epitheliumwould not make its appearance until the full-term stage.No complete occlusion was observed in the esophagus and small intestineduring the embryonic period as remarked by some authors.This may be as-cribed to the individual deviation of the specimens during embryonic develop-ment.A comparative study of the digestive tracts of animals of different feedinghabits,such as monkey,rabbit,bat,weasel and domestic cat,were also madein the course of the present study in order to elucidate their histologicaldifferences.Segments of different parts of the digestive tract obtained fromeach animal were fixed and sectioned by routine procedure.Sections of eachsegment of the specimens were specifically stained with H.E.,I.H.,Mallory'striple staining method,Masson's method for argentaftin cells,and phosphc-tungstic acid and hematoxylin method for Paneth's cells.In general the morphological constitutions of the epithelium of the di-gestive tract of the corresponding parts were found to be fundamentallysimilar in the following aspects:the presence of the stratified squamousepithelium of the esophagus,the simple columnar epithelium of the stomach and intestine,the villi of the intestine,the intestinal glands and the gobletcells of the small and large intestines,and the striated border of the smallintestine,etc.The following differences were noted among the specimens studied;theparietal cells were comparatively few in number in the fundus of the monkey'sstomach and the goblet cells were absent in the rabbit's large intestine.Paneth's cells were quite common in the fundus of the intestinal glandsof man,cat and bat;but they were not found in the monkey,rabbit andweasel.The argentaffin cells were often found in scattered manner in theepithelium of the intestinal gland of the small and large intestines in man,bat and weasel,and they were also found in the bottom of the gastric glandin the monkey,but were absent in the entire digestive tract of the rabbit.