The Phylum Vertebrata in the above scheme branches into the sub-phyla Hemichorda, Urochorda, Cephalochorda and Craniata.
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.
This assemblage is now generally regarded as a great division (phylum or sub-phylum) of the animal kingdom and known by K.
For the class of the true insects included in this phylum, Linnaeus's old term Insecta, first used in a restricted sense by M.
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.