An ultrastructural description of the cell types in the endocrine pancreas of the pigeon.

We describe completely the electron-microscopical aspects of the endocrine pancreas in the pigeon. The general characteristics of this organ coincides with that found in granivorous birds and consist of D, A, B, IVth type of cells and acinar-D cells. The D cells are electron-dense and contain many large spheric secretory granules with an adherent membrane. The A cells are spheric or columnal, having few cell organelles, a low electron-density and contain spheric or oval secretory granules with a narrow space between their membrane and content. The B cells are elongated, electron-dense, have many cell organelles and contain numerous polymorphic secretory granules with a crystallized content and a halo between the membrane and their content. The IVth type of cell described for the first time in the pigeon is small, has a low electron-density, a large nucleus, few and very small secretory granules. These cells are placed marginally in the islet. The acinar-D cell is also for the first time found in pigeon and is represented by cells where predominate the acinar component or the endocrine D component.