Granulopoiesis in tadpoles of Rana esculenta. Ultrastructural observations on the morphology and development of heterophil and basophil granules.

The morphology and development of heterophil and basophil granules from the trunk kidneys of Rana esculenta tadpoles were studied at the electron microscopic level. Cells of the heterophils series contain granules displaying either spheroid profiles with homogeneous content (Type A), or elongate profiles with a crystalloid interior (Type B). Type A granules apparently originate directly from Golgi-derived vesicles, which, gaining slightly in size and density, transform into the mature granules. Type B granules could be traced back to vacuolate structures showing an irregular content. Their development could be traced through increasingly elongated forms with the appearance of a characteristic crystalloid core. Fully developed basophil granules are considerably larger in size than heterophil granules and contain heterogeneous interna showing a central-cortical organisation: a finely stippled medullary zone of varying density is surrounded by a sickle-shaped and lamellate cortex (Type L), or a moderately dense and uniformly stippled medulla is enclosed by two diametrically opposed, cap-shaped, filamentous regions (Type F). The heterophil and basophil granules are compared to those in other vertebrates and possible phylogenetic aspects are discussed.