It is maintained that insects and their allies, Symphylids and Chilopods, have descended directly from Polychaete annelids somewhat remotely related to Worthenella cambria Walcott from the Middle Cambrian of British Columbia, and that neither the Crustaceans, as suggested by Muller (1864), nor the Campodeans through the Myriopods and Onychophorans, as held by Brauer (1868) and others, are in the direct line of descent. The general argument so far as external form is concerned is based on the relation of the parapodium of the polychaetes to the thoracic appendages and pleurites of the insects. The episternal-epimeral area is considered as the proximal part of a parapodium which has rotated clockwise some 45[degree], as viewed from the left, and fused with the body, while the coxa formed of the coxon and meron with the remaining segments of the leg represents the distal part of the parapodium, particularly the neuropodium. Such an explanation is consistent with the ecological conditions under which many of the polychaete worms lived in the marshy areas of coastal regions. The para-podia would be more and more compelled to support the body as the individual moved through the shallow and partially dried pools, the lower branch or neuropodium attaining a greater development than the upper branch or notopodium. It is suggested that the wings of insects developed from cirri at the base of the para-podia. Accordingly, Arthropods are considered as wholly an artificial group and the Thysanurans as not in the direct ancestral line of the winged insects. Closely associated as a group are the Pterygotes, Thysanurans, Collembolans, Proturans, Symphylids, and Chilopods. More remotely related are the Diplopods, Pauropods, and Onychophorans.