Phylum synonyms

The terms used for indicating groups are " Phylum " for the large diverging branches of the genealogical tree as introduced by Haeckel, each Phylum bears secondary branches which are termed " classes," classes again branch or divide into orders, orders into families, families into genera, genera into species.

The Phylum Appendiculata similarly branches into sub-phyla, viz.

Vertebrate palaeontologists were slow to grasp this principle; while the early speculative phylogenies of the horse of Huxley and Marsh, for example, were mostly displayed monophyletically, or in single lines of descent, it is now recognized that the horses which were placed by Marsh in a single series are really to be ranged in a great number of contemporaneous but separate series, each but partially known, and that the direct phylum which leads to the modern horse has become a matter of far more difficult search.

They are not, therefore, like the wings of birds, modified from some pre-existing structures (the fore-limbs) common to their phylum; they are new and peculiar structures.

The inter-relationships of the three members of the Platyelmia are of a more doubtful nature than is the unity of the phylum.