There is no reason to suppose that any of the forms of limb observed in Arthropoda may not have been independently developed in two or more separate diverging lines of descent.
SUB-Phylum Arthropoda (of the Phylum Appendiculata).
Hence the term Appendiculata was introduced by Lankester (preface to the English edition of Gegenbaur's Comparative Anatomy, 1878) to indicate the group. The relationships of the Arthropoda thus stated are shown in the subjoined table: - (Sub-phylum r.
They have appeared independently in connexion with a change in the excretion of nitrogenous waste in Arachnids, Crustacea, and the other classes of Arthropoda when aerial, as opposed to aquatic, respiration has been established - and they have been formed in some cases from the mesenteron, in other cases from the proctodaeum.
The Insecta of Linnaeus was a group exactly equivalent to the Arthropoda founded a hundred years later by Siebold and Stannius.
It is a noteworthy fact that other tubes in these same terrestrial Arthropoda - namely, the ducts of glands - are similarly strengthened by a chitinous cuticle, and that a spiral or annular thickening of the cuticle is developed in them also.
It differs, however, from all other Arthropoda in such important respects that a special class, equivalent in rank to the old-established Arthropod classes, had been created for its sole occupancy.
The class Insecta of Linnaeus (1758) was coextensive with the Arthropoda of modern zoologists.
The solid palpless mandible such as we now see in some Arthropoda is, necessarily, a late specialization.
His order of wingless insects (Aptera) included Crustacea, spiders, centipedes and other creatures that now form classes of the Arthropoda distinct from the Hexapoda; it also included Hexapoda of parasitic and evidently degraded structure, that are now regarded as allied more or less closely to various winged insects.