Definitions

from The Century Dictionary.

  • A hypothetical group of worm-like animals, of which the chordonium is the type or common parent-form, and of which the tunicate Appendicularia or any caudate ascidian larva is an extant representative, distinguished primarily by the possession of a notochord in the form of a urochord, and supposed to be the immediate progenitors of the ascidians and vertebrates.

Etymologies

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Examples

  • In view of its sound establishment and its profound significance, it may very well claim to be a THEORY, and so should be described as the chordonia or chordaea theory.

    The Evolution of Man — Volume 2

  • Tunicates and Acrania have inherited the chorda from a common unsegmented stem-form; and these ancient, long-extinct ancestors of all the chordonia are our hypothetical Prochordonia.

    The Evolution of Man — Volume 2

  • The tenacity with which the useless neurenteric canal has been transmitted down to man through the whole series of vertebrates is of equal interest for the theory of descent in general, and the phylogeny of the chordonia in particular.

    The Evolution of Man — Volume 1

  • Hence we may conclude, according to the laws of the theory of descent, that all these chordonia or chordata (tunicates and vertebrates) descend from an ancient common ancestral form, which we may call Chordaea.

    The Evolution of Man — Volume 1

  • (Figures 1.83 to 1.86) provides a valuable support of our phylogeny; it indicates the important moment in our stem-history at which the stem of the chordonia (tunicates and vertebrates) parted for ever from the divergent stems of the other metazoa (articulates, echinoderms, and molluscs).

    The Evolution of Man — Volume 1

  • Among these worms we find some important forms that show considerable advance in organisation from the platode to the chordonia stage.

    The Evolution of Man — Volume 2

  • From the evolutionary point of view the coelom-pouches are, in any case, older than the chorda; since they also develop in the same way as in the chordonia in a number of invertebrates which have no chorda

    The Evolution of Man — Volume 1

  • Even then the egg was first a gastraea-egg, then a platode-egg, then a vermalia-egg, and chordonia-egg; later still acrania-egg, then fish-egg, amphibia-egg, reptile-egg, and finally bird's egg.

    The Evolution of Man — Volume 2

  • Next to the ancient stem-group of the Turbellaria come a number of more recent chordonia ancestors, which we class with the Vermalia or

    The Evolution of Man — Volume 2

  • The coelom-pouches were originally sexual glands in these ancient chordonia.

    The Evolution of Man — Volume 1

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