The ultrastructure and cytochemistry of the shell membrane‐secreting region of the Japanese quail oviduct

The isthmic mucosa or shell membrane‐secreting portion of the Japanese quail oviduct was examined by light and electron microscopy and by cytochemical techniques. Preliminary studies of the shell membrane were also made. The mucosa of the isthmus is thrown into numerous longitudinal folds which are covered by a simple columnar epithelium consisting of ciliated and mucussecreting cells. Numerous convoluted simple tubular glands lie densely packed beneath the surface epithelium and are connected to it by short ducts. The tubular glands are made up of a single cell type, the principal cell, which contains numerous large secretory granules. Mature granules display an eccentrically placed dense spherical core surrounded by a less dense cortex. The shell membrane is composed of a meshwork of intersecting fibers oriented randomly in the plane of the membrane; each fiber is made up of a medulla and cortex. Cytochemical methods indicate that the principal cell secretory granules consist of a complex of carbohydrate with protein. The protein is rich in sulfhydryl groups; the polysaccharide moiety is neither sulfated nor rich in carboxyl groups. The mucigen granules are composed of a nonsulfated carbohydrate‐containing substance. The shell membrane has both carbohydrate and protein components. Speculations are presented on the morphological relationships between the various components of the completed shell membrane and their secretory precursors.