Ultrastructure and Differentiation of Hydrodictyon Reticulatum IV. Conjugation of Gametes and the Development of Zygospores and Azygospores

Abstract

In H. reticulatum, gametes differed from other zooids principally in that some of them bore an electron·dense apical cap between their flagella. Conjugation did not take place until the walls of the coenobia, in which the gametes developed, ruptured; and often did not occur even among the liberated gametes. Only in zooids collected from cultures in which conjugation was evident were these apical caps extended as fertilization tubules. Fertilization took place by the fusion of the tip of this tubule on one gamete with the membrane between the flagella of another which apparently lacked a fertilization tubule. Subsequent lateral fusion of the united zooids produced quadriflagellate zygotes which were active for only a short time before flagellar retrac· tion and cell wall deposition. Karyogamy usually preceded wall secretion. Gametes failing to conjugate often laid down a wall to form azygotes.