Morphologie und Schwimmbewegungen der erwachsenen Anthomedusen. Entwicklung von der Eifurchung bis zum planktischen, sternchenförmigen Stadium der Proactinula: totale plan-parallele Furchung, "schneidende" Furchung, direkte Entwicklung ohne das Stadium der planktischen, begeißelten Planula. Differenzierung der jungen Meduse bis zum geschlechtsreifen Tier.

Development of the Hydrozoon Ectopleura dumortieri (Athecatate-Anthomedusae). The metagenetic species Ectopleura dumortieri (Van Beneden, 1844) belongs to the Hydroida Athecata, family Tubulariidae. The sessile polyp is solitary; the medusa is fairly abundant in the summerplankton of the southern North Sea: First, the film demonstrates the morphology of the adult medusa and its swimming movements, and then, time-lapse movies reveal the complete development from the beginning of the egg cleavage to the formation of the planktonic starlet shaped stage of the proactinula. The special mode of development is characterized by: a) the total plane-parallel cleavage to the stage of 32 cells which represents one long row of blastomeres; b) the cutting cleavage furrows which sharply divide the cells successively from one pol to the other as with a knife; a) the direct development from the egg to the proactinula because the normale stage of the free-swimming planktonic flagellated planula is completley suppressed.