Animals were placed in a room in which the normal light-dark sequence was reversed for at least 4 days. Three or four females were placed with a male in total darkness. Copulation was determined by the presence of a vaginal plug. The middle of the “artificial night” was designated as day 0 of pregnancy. It is not considered identical with ovulation time. A late ovulation may result in considerable retardation in development. On the other hand, an early ovulation does not advance development, because the second maturation division is completed only after fertilization.


Human Embryo Total Darkness Vaginal Plug Stage Number Hybrid Embryo 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Copyright information

© Springer Science+Business Media New York 1989

Authors and Affiliations

  • Karl Theiler
    • 1
  1. 1.Department of AnatomyUniversity of ZurichZurichSwitzerland

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