Since the publication of my monograph "Die submikroskopische Struktur des Cytoplasm as" [Protoplasmatologia III A12 (1955)], science has increased our knowledge on this cell constituent in an amazing way. At that time, cytoplasm was still considered as an amorphous colloid with an amicroscopic structure capable of sol/gel transformations. Meanwhile, within the past 18 years, ultrastructure research and molecular biology have shown that it consists of structured organelles, thereby revolutionizing our concept of the cytoplasm. There is an ontogeny of these organelles which deals with their appearance, development, growth and eventual disappearance. Although the results of relevant studies are less spectacular at this time than those concerning nucleic acids, they will become