from Wiktionary, Creative Commons Attribution/Share-Alike License

  • adj. Without a placenta, as marsupials and monotremes.
  • n. A mammal having no placenta.

from the GNU version of the Collaborative International Dictionary of English

  • adj. Without a placenta, as marsupials and monotremes; nonplacental.

from The Century Dictionary and Cyclopedia

  • Having no placenta; not placental; specifically, pertaining to the Implacentalia or having their characters. Also implacentate.
  • n. An implacental mammal, as a marsupial or a monotreme.


im- +‎ placental? (Wiktionary)


  • Lemuroid and the higher forms of primates; for those between the original primate and other root-forms of placental mammals; for those between primary placental and implacental mammals, and perhaps also for the divergence of the most ancient stock of these and of the monotremes, for in all these cases modifications of structure appear to increase in complexity in at least that ratio.

    On the Genesis of Species

  • Remarkable similarities between certain placental and implacental mammals, between the bird's-head processes of

    On the Genesis of Species

  • Again, the implacental mammals, including the Ornithodelphia and the Marsupials, are admitted to be lower than the placental series.

    Contributions to the Theory of Natural Selection A Series of Essays


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