The role of polarity in the development of the hydrozoan planula larva

  • Gary Freeman

DOI: 10.1007/BF00867804

Cite this article as:
Freeman, G. Wilhelm Roux' Archiv (1981) 190: 168. doi:10.1007/BF00867804


These experiments were done in order to define the role that polarity plays during embryogenesis in hydrozoans.

Parts of hydrozoan embryos isolated at different developmental stages from early cleavage to postgastrula will regulate to form normal planulae. During this process, the original anterior-posterior axis of the part is conserved. In normal embryos the posterior pole of the anterior-posterior axis is congruent with the site where the polar bodies are given off and with the site where the first cleavage is initiated. By centrifuging fertilized eggs, it is possible to create embryos in which the first cleavage initiation site does not correspond to the site where the polar bodies are given off. In these embryos the posterior pole of the anterior-posterior axis corresponds to the first cleavage initiation site. When parts of these embryos are isolated at different stages they also regulate to form normal planulae. The axial properties of these planulae are determined by the site of first cleavage initiation.

The interactions between regions of the embryo with different axial properties were studied by grafting together parts in such a way as to create embryos with abnormal axial arrangements. Following gastrulation interactions take place between the grafted parts leading to the formation of normal planulae with a new set of axial properties.

Blastula stage embryos can be dissociated into single cells and the cells can be reaggregated. These reaggregates form normal planulae. Polarity can be entrained in the reaggregates by grafting a small piece of tissue from any part of an intact blastula to the reaggregate. These cells organize the formation of an axis of symmetry with an appropriate orientation with respect to the graft.

Key words

Embryogenesis Polarity Regulation Hydrozoan 

Copyright information

© Springer-Verlag 1981

Authors and Affiliations

  • Gary Freeman
    • 2
    • 1
  1. 1.Friday Harbor LaboratoriesUniversity of WashingtonUSA
  2. 2.Department of ZoologyUniversity of Texas at AustinAustinUSA

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