Description:
<jats:p> The ultrastructure of normal and neoplastic mast cells of the cat was compared. Granules of normal mast cells were more heterogeneous than those of neoplastic mast cells, although their substructures were similar. Normal mast cell granules contained electron-dense cord-like structures, reticulum, strands, or dense cores. Crystalline structures were seen in a few granules. Neoplastic mast cells contained many cell organelles and intracytoplasmic fibrils. Small granules thought to represent earliest forms of mast cell granules were present in the Golgi zones of neoplastic mast cells from one cat only. Maturation of mast cell granules in the cat resembled that in the rat. The comparative ultrastructure of feline mast cells and those of other species is discussed. </jats:p>