LEE BARKER WALTON 171 



type which are evidently of a primitive nature and that 

 definite relationships with such Symphylids as Scolopen- 

 drella and Sciitigerella are clearly indicated, it is by no 

 means necessary to insist that the winged insects have 

 developed from such a type. The aerial life which they 

 lead in general has permitted the retention of the cylin- 

 drical body and at the same time the parapodial structure. 

 Insects without wings, as well as many of those with 

 wings which need protection by leading a terrestrial life 

 as opposed to an aerial existence, have become much flat- 

 tened dorso-ventrally and the pleurum correspondingly 

 modified. The pleural regions of the Thysanurans as 

 well as the thoracic regions of the Coleoptera, the Blat- 

 tidae, etc., illustrate this. 



The evidence presented, fragmentary as it is, appears 

 to point definitely to the conclusion that the various 

 groups of insects and their allies have evolved directly 

 jfrom the Polychaete worms, and that the parapodium is 

 the fundamental structure from which not only the ap- 

 pendages and pleurites of the thorax but also the appen- 

 dages and pleurites of the cephalic and caudal regions 

 have developed. Furthermore, there is evidence in favor 

 of the theory that the wings have originated from basal 

 parapodial appendages quite different in position from 

 those modified as tracheal gills in existing insects. From 

 the systematic side one therefore concludes that the An- 

 nulates form a definite phylum, the Annularia, consisting 

 of a series of classes among which are the insects and their 

 allies, and that the Arthropods are wholly an artificial 

 group. We may enumerate these classes as the Pterygotes, 

 the Thysanurans, the Collembolans, the Proturans, the 

 Symphylids, and the Chilopods. More remotely related 

 to the insects are the Diplopods, the Pauropods and the 

 Onychophorans. 



In order to eventually establish the course of evolution 

 among the insects paleontological material must be pro- 

 cured. The extremely well-preserved forms, such as 

 Worthenella, Aysheaia, etc., obtained by Walcott from 

 the Burgess Shales of British Columbia, indicate that it 

 is here that efforts to obtain such material should be made 



