Cytochemical Evidence for an Ultimobranchial Origin of Rodent Thyroid C Cells

THE cells referred to in this communication were called parafollicular cells by Nonidez 1 in dog thyroid. The name was afterwards transferred to cells staining in a similar manner in other species, irrespective of their anatomical position. It was condemned by Stux et al. 2 as inaccurate. They substituted the name light cell because, in rat thyroid, the cells are not stained by the periodic acid–Schiff (PAS) method by comparison with the colloid granules of the acinar cells. The name C cell 3 was intended to refer to their responsibility for calcitonin secretion, as indicated by cytochemical tests and by immunofluorescence 4 . It avoids reference to the staining qualities of the cells and to their precise localization, and for this reason it can be applied to all species and to organs and tissues other than the thyroid. Not only are the cells not parafollicular, they are not confined to the thyroid 5 and in some species are probably mainly extra-thyroid.