Morphology, histochemistry and biochemistry of the oviduct of the toad, Bufo vulgaris (Anura, Amphibia), during the annual reproductive cycle.

On the basis of histological and histochemical characteristics the oviduct of adult Bufo vulgaris can be separated into six zones. These characteristics include mainly the relative abundance of secretory and ciliated epithelial cells, mucosal foldings, tubular glands and the staining properties of the secretory elements. The VI zone (uterine segment) is totally deprived of tubular glands and is profoundly rich in epithelial secretory cells. These cells and the tubular glands, when well-developed, are rich in neutral and acid mucins in the preovulatory phase, whereas this content is greatly diminished after ovulation. Similarly, the weight and the length of the oviduct displays a marked seasonal pattern. The same is observed for its protein content and acid and alkaline phosphatases. These parameters show the highest values in the preovulatory period and lowest after ovulation. The toad oviduct also displays marked hydroxysteroid dehydrogenase activity along the mucosal epithelium. Its functional significance remains a matter of debate, however. A marked parallelism between the present data and those obtained by others in other amphibians indicates the existence of a common pattern of seasonal modifications correlated mainly with the release of the eggs and the formation of their multi-layered coat.