On the ether hand, a survey of the facts of cellular embryology which were accumulated in regard to a variety of classes within a few years of Kovalevsky's work led to a generalization, independently arrived at by Haeckel and Lankester, to the effect that a lower grade of animals may be distinguished, the Protozoa or Plastidozoa, which consist either of single cells or colonies of equiformal cells, and a higher grade, the Metazoa or Enterozoa, in which the egg-cell by " cell division " gives rise to two layers of cells, the endoderm and the ectoderm, surrounding a primitive digestive chamber, the archenteron.   anvd [Please select]

The phylum Porifera or Spongiæ includes the simplest of the Metazoa or multicellular animals.   anvd [Please select]

From the compound Protozoa its members are distinguished by the fact that the cells of which they are composed exhibit considerable differentiation both in structure and in function, and are associated together in a definite manner, although they are not combined to form organs and systems of organs as in the higher Metazoa.   anvd [Please select]

The second of the great groups or phyla into which the metazoa are divided is the Coelenterata, in which are included most of the animals commonly known as zoophytes, and also the corals, sea-anemones and jelly-fish.   anvd [Please select]