ABSTRACT
The ultrastructure of the adrenal medulla in adult laboratory animals has been described in a number of reports (Lever, 1955; Sjôstrand & Wetzstein, 1956; Wetzstein, 1957; de Robertis & vaz Ferreira, 1957; Erânkô & Hânninen, 1960; Yates, 1963, 1964a, b, c;Coupland, 1965a, b; Elfvin, 1965a, b). Since the introduction of the glutaraldehyde fixation technique, it has been possible to distinguish clearly between cells storing adrenalin and those storing noradrenalin by the different densities of their granules (Coupland, Pyper & Hopwood, 1964; Coupland, 1965 a; Elfvin, 1965 a). In order to study the histophysiology of the secretory process of catecholamines, suprarenal glands have been investigated under normal conditions and under the influence of mechanical, physical and chemical-pharmacological agents (the above references and Graf, 1966). The purpose of the present investigation was to study the structure of adrenal medulla of the rat during the prenatal period and to relate the findings to the process of secretion in the medullary cells.
