[The inner surface of chick embryo small intestine by scanning electron microscope]

The inner surface of the midgut of chick embryos aged seven to fifteen days of incubation has been examined by scanning electron microscopy. At this period, the surface of the mucous membrane undergoes significant morphological changes; in fact, while at seven days of incubation it appears to be smooth and regular, in the following days it begins to show longitudinal folds increasingly higher, more numerous and complicated. After eleven days of incubation some folds take a zig-zag appearance that progressively becomes more evident and extends to all the folds. In the mean time, the enterocytes undergo a gradual differentiation and represent the only type of epithelial cells at this stage of development. Their apex until seven days of incubation is dome-shaped, provided with short microvilli and separated from the surrounding cells by deep circular grooves. At about thirteen days the apex appears to be less swollen, with longer and more numerous microvilli and delimited by microplicae arranged in a hexagonal disposition.