title: The influences of ecto- and endoderm in determining the axial polarity ofHydra attenuata Pall. (Cnidaria, Hydrozoa).
abstract: Ectoderm and endoderm of the gastric column ofHydra attenuata Pall. were separated from each other and reassembled with either the same (controls) or opposite polar orientation. The controls always regenerated a head and basal disc according to the original polarity. In those specimens in which the polarity of ecta- and endoderm was opposite 33 specimens out of 41 reconstituted a single polyp whose body axis was clearly identifiable. Of these cases 8 followed the polarity of the ectoderm, 3 obeyed that of the endoderm, and 22 formed axes perpendicular to the original longitudinal axis. In 5 cases 2 specimens regenerated from the reassembled specimens. It is thus demonstrated that axial polarity ofHydra is determined by both the ecto- and the endoderm.
authors.affiliation: Zoological Institute, University of Zürich-Irchel, Winterthurerstrasse 190, CH-8057, Zürich, Switzerland.
authors.forename: Iris
authors.initials: I
authors.lastname: Smid
authors.affiliation: Zoological Institute, University of Zürich-Irchel, Winterthurerstrasse 190, CH-8057, Zürich, Switzerland.
authors.forename: Pierre
authors.initials: P
authors.lastname: Tardent
keywords: Hydra attenuata; Morphogenetic gradients; Polarity; Recombination of ecto- and endoderm