Ultrastructure and Differentiation of Hlydrodictyon Reticulatum VI. Formation of the Germ Net

Abstract

Uninucleate, biflagellate, net-forming zoo ids arise by cleavage of the multi-nucleate cytoplasm of polyhedra. These zoo ids appeared to be indistinguishable from net-forming zooids produced by cylindrical coenocytes. Whereas zoo ids derived from cylindrical cells aggregated within their parental cell wall to form cylindrical nets, zooids produced by polyhedra swarmed within a spheroidal vesicle, probably derived from the inner layer of polyhedral wall, and aggregated usually as a flat net, similar to nets of other species of Hydrodictyon and vegetative colonies of Pediastrum. Bands of peripheral microtubules underlaid the initial sites of contact of aggregating zooids; the role of these microtubules, which were generally oriented in the plane of the developing net, and other aspects of patterned cellular aggregation are discussed.