Lanzettfischchen. Habitus, Gonaden. Ausstoßen der Geschlechtsprodukte, Spermien, Befruchtung, Befruchtungsmembran, inäquale Furchung, Blastula, Gastrulation (Invagination), Bewegung des Embryos in der Eihülle, Streckung des Keims, Schlüpfvorgang, Schwimmen des Embryos, Entwicklungsstadien an festgelegten Tieren (Organogenese), Fortbewegung der Larve.

This film provides scenes of the embryonic development of the Branchiostoma lanceolatum. Initial scenes show the habitus and gonades of adults. Females are clearly distinguishable from males due to the large number of eggs in the ovaries under the binocular. These scenes are followed by those of sperms, which are among the smallest in the species of the chordates. When a sperm manages to penetrate an egg, this lifts away from the insemination membrane, which forms a transparent protective sheath through the intake of water. A fertilized and an unfertilized egg are shown. Approximatel one hour after fertilization the weak inequal furrowing commences. After gastrulation takes place the embryo starts moving inside the egg sac, since each ectoderm cell has a cilium. Depeding on size and dimension of the embryo various movements take place: turning through the body's cross axis, rotation through the body's long axis. If 2 or 3 primary segements have formed the embryo bursts the egg sac. Emergence and subsequent swimming are shown at normal speeds. In closing single phases of further embryonic development are shown in certain animals. After approximately 48 hours embryonic development is completed. Thy young larvae, in which chorda, mouth opening and the 1st gill opening are now formed, reach the ocean bed by means of varying snakelike movements or simple gliding, once here they commence a complicated process of metamorphosis.