The development of the chick embryo gallbladder studied by scanning electron microscope.

The differentiation of the gallbladder mucous membrane in chick embryos has been studied from the 11th day of incubation until hatching (stages 37-46 of Hamburger an Hamilton 1951) with scanning electron microscope. The surface of the mucous membrane, at the 11th day of incubation, appears regularly smooth. From the 12th day onwards, longitudinal folds appear on the surface of the mucous membrane, becoming more and more numerous and complicated in the following days. During the last days of incubation, branching and anastomosing folds are present. At the 11th day of incubation, the epithelial cells lining the gallbladder surface have flattened apices, with short microvilli. From the 12th day onwards, the epithelial cells show dome shaped apices, with long numerous microvilli. From the 15th day of incubation onwards, some particular secretory cells can be detected. The appearance of these cells is probably related to the water-absorbing function of the gallbladder which in the last days of incubation completes its functional development, because of precise digestive requirements of the chick embryo.