Fine structure and development of the zygospore of Rhizopus sexualis (Smith) Callen

The development of the zygospore of Rhizopus sexualis (Smith) Callen was followed by light microscopy, transmission electron microscopy and scanning electron microscopy. Details of all stages, including dissolution of the fusion wall, delimitation of the gametangia by septa, and formation of the complex wall of the zygospore are described and illustrated. Changes in number, form and distribution of the organelles and the behaviour of the nuclei are described. The probable function of the cytoplasmic organelles and the possible mechanisms controlling development are discussed.