The four histological methods, previously known to be useful in selective detection of endocrine cells, were applied to the duck digestive tracts, from oesophagus to colorectum. Cells stained with lead-hematoxylin and HC1-toluidine blue were observed in all regions of the duck digestive tracts with the exception of the oesophagus. Argyrophil cells were observed in proventricular mucosa and glands, and in the intestine. Argentaffin cells were observed only in the intestine.
The frequency of endocrine cells in the duck digestive tracts was highest in the restricted region of gizzard mucosa where was called the pyloric region in this paper, next in the proventricular glands, equally about half of the frequency in the pyloric region in the five regions of the intestine, one tenth of that of the proventricular glands in the proventricular and isthmus mucosa, and the smallest frequency was noted in the central part of gizzard mucosa.
The pyloric region was about 5mm anterior to the narrow mucosal fold separating the gizzard from the intestine. It was an interesting to find that the endocrine cells which were nonargentaffin and nonargyrophil were densely present in this region.
From the staining properties and the distribution of the endocrine cells, the possibility of existence of four and more types of endocrine cells in the duck digestive tracts was discussed.