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It embraces several subkingdoms, and under these there are Classes, Orders, Families, Genera, Species, and sometimes intermediate groupings, all in regular subordination, but variously arranged by different writers.

These three classes or subkingdoms, as perhaps they might be termed from analogy with systems of biological classifications, are in technical language: 1.

Regards Protozoa as subkingdom and the four great divisions as phyla.

The communication between individuals is especially characteristic of vertebrates, and in the higher members of that subkingdom it plays a very great r�le in aiding the work of consciousness.

In the Cambrian, Ordovician, and Silurian the invertebrates were represented in all their subkingdoms by a varied fauna.