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During embryogenesis, cardiac myocytes have many cytological characteristics of secretory or glandular cells . Early embryonic ventricular myocardial cells have a large amount of granular endoplasmic reticulum and a well-developed Golgi complex, and these cells have been implicated in the elaboration of cardiac jelly (7) . Indeed, evidence is accumulating that indicates that cardiac muscle has a secretory role in the adult, as well as in the embryo . For example, Lockett (6) has provided physiological evidence for the secretion of a humoral agent by mature myocardium . In an earlier electron microscopic study, Jamieson and Palade (4) described the presence of membrane-bounded granules associated with the Golgi region of mature atrial muscle cells of several mammalian species . More recently, Hibbs and Ferrans (3) reinvestigated rat atrial granules, employing histochemical as well as electron microscopic techniques. During the course of a comparative study, Trillo et al . (11) noted that both atrial and ventricular muscle cells of the chick contain approximately the same number of secretory granules . They have also been described in ventricular muscle cells of toads (8), cyclostomes (1), and frogs (10), and, in fewer numbers, in rat ventricular muscle (11) . Little is known about the time of appearance and distribution of myocardial granules during embryonic development . Jamieson and Palade (4) noted their presence in late fetal and neonatal rats, but not in a 10 mm embryo, and Pager (9) conBRIEF NOTES

THE APPEARANCE OF GRANULES IN THE GOLGI COMPLEX OF EMBRYONIC CARDIAC MYOCYTES