The introduction of light and especially electron optic systems for morphological studies of cellular and subcellular structures has enabled significant advances to be made in the knowledge of cell biology and normal and diseased organs.Molecular aspects of cellular processes and the functional or evolutionary significance of the increasing complexity of higher organisms cannot be elucidated simply by comparing fine structures. In this context, histochemical and new specific molecular staining procedures allow relationships between biological structure and function to be more readily discerned.