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Rh same range and distinctive character as every other, nor to make such a proposition about classes, orders, families and genera. Where a further subdivision is desirable without descending to the next lower term of grouping, the prefix "sub" is made use of, so that a class may be divided first of all into subclasses each of which is divided into orders, and an order into sub-orders each of which bears a group of families. The term "grade" is also made use of for the purpose of indicating the conclusion that certain branches on a larger or smaller stem of the genealogical tree have been given off at an earlier period in the history of the evolution of the stem in question than have others marked off as forming a higher grade. Thus, to begin with, the animal pedigree is divided into two very distinct grades, the Protozoa and the Metazoa. The Metazoa form two main branches; one, Parazoa, is but a small unproductive stock comprising only the Phylum Porifera or Sponges; the other, the great stem of the animal series Enterozoa, gives rise to a large number of diverging Phyla which it is necessary to assign to two levels or grades — a lower, Enterocoela (often called Coelentera), and a higher, Coelomocoeta (often called Coelomata). These relations are exhibited by the two following diagrams.





The Phylum Vertebrata in the above scheme branches into the sub-phyla Hemichorda, Urochorda, Cephalochorda and Craniata. The Phylum Appendiculata similarly branches into sub-phyla, viz. the Rotifera, the Chaetopoda and the Arthropoda. Certain additional small groups should probably be recognized as independent lines of descent or phyla, but their relationships are obscure—they are the Mesozoa, the Polyzoa, the Acanthocephala and the Gastrotricha.

We may now enumerate these various large groups in tabular form.

A statement may now be given of the classes and orders in each group, as recognized by the writers of the various special zoological articles in the Eleventh Edition of the Encyclopaedia Britannica. These subdivisions of the larger groups are not necessarily those theoretically approved by the present writer, but they have the valuable sanction of the individual experts who have given special attention to different portions of the vast field represented by the animal kingdom.