To clarify the formation of egg-coverings in birds, the isthmus, isthmouterine region and uterus of quail oviducts and their egg-coverings were investigated histologically. The obtained results are as follows.
1. Mucous cells proper to the isthmouterine region are termed as isthmouterine mucous cells. Their features are different from the isthmal and uterine mucous cells. The isthmouterine mucous cells are characterized by high stainability for lipoprotein reaction.
2. Stratification of decalcified quail egg-coverings and structures of each layer of them are similar to those of hen's eggs. The mammilla is divided into central core and superficial portion.
3. Neutral mucopolysaccharides are present in the shell membranes, central core of the mammilla and cuticle; acid mucopolysaccharides in the superficial portion of the mammilla and shell matrix.
4. The central core contains a certain amount of concentrated lipoprotein.
5. The author discussed the interelationship between the oviducal secretions and the constituents of the egg-coverings, on the basis of findings reported in previous and present papers.