Metazoa n. pl. (Zool.) Those animals in which the protoplasmic mass, constituting the egg, is converted into a multitude of cells, which are metamorphosed into the tissues of the body. A central cavity is commonly developed, and the cells around it are at first arranged in two layers, the ectoderm and endoderm. The group comprises nearly all animals except the Protozoa.
... of the true many-celled animals, or Metazoa, where the biological units are combined to form an organic association displaying many more resemblances to a human society. The freshwater polyp Hydra, like the foregoing illustrations, is one whose structure has already been discussed in the earlier chapters, but now we may use ... — The Doctrine of Evolution - Its Basis and Its Scope • Henry Edward Crampton
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