Observations were made on the pancreatic islets of the snake, Elaphe climacophora, and a teleost, yellow-tail or Seriola quinqueradiata, using alternate thick and thin sections for light and electron microscopy.
Under the light microscope, the snake islets contain A-cells with red-stained secretory granules and B-cells with blue-stained granules. The islets of the yellow-tail consist of A-cells with red granules, B₁-cells with dark blue granules, B₂-cells with light blue granules and C-cells without granules (modified aldehyde thionine-hematoxylin-phloxin B).
Electron microscopy indicates that the A-cells of the snake islets contain both small dense and large, less dense granules. B-cells are divided into two types, one of which contains dense spherical granules whereas the other, less dense crystalline ones. Some crystalline granules show a hexagonal shape and a lamellar structure with a periodicity of about 90Å.
The yellow-tail islets contain five different cell types; A, B₁, B₂, C₁ and C₂ cells. The A-cells contain dense spherical granules. The B₁-cells possess dense crystal granules, some of which are hexagonal in shape like the B-cell granules of the snake. The B₂-cells contain less dense amorphous granules. The C₁-cells usually show empty vacuoles, whereas the C₂-cells contain no secretory granules. Transitional cells occur between B₁, B₂ and C₁ cells and between A and C₂ cells, suggesting that they represent functionally different states of the B and A cells rather than different cell types.
The eruptocrine or Type IV extrusion of crystalline granules of the yellow-tail B-cells was clearly shown.