The development of the glandular stomach was studied using light, electron, and fluorescent
microscopy. The research used 130 Japanese quail eggs from the second to the seventeenth days of
incubation.The proventriculus could be distinguished on the3rd day. Its wall consisted of four tunics:
tunica mucosa, very thin tunica submucosa, tunica muscularis, and outermost tunica serosa. Mucosal
folds appeared on the 8th day. The luminal epithelium was pseudostratified columnar in type and
transformed into simple columnar by the 10th day. The mucosal papillae emerged on the 11th day,
spiraled on the 15th day, and had a distinct whorled look by the 17th day. Two types of proventricular
glands were recognized: compound tubuloalveolar and simple tubular glands. Both types were
situated within the tunica mucosa. On the 4th day, the compound glands emerged as evaginations
of the lining epithelium. It began to branch on the 8th day and became well established by the 11th
day. The simple glands appeared on the 11th day as localized down-growths of the luminal epithelium
forming solid cords. On the 15th day, many of them showed complete canalization. On the 8th day,
the muscular coat was differentiated into the lamina muscularis mucosae and tunica muscularis.