LEE BARKER WALTON 167 



trachea, would tend to occupy a position outside of the 

 parapodial area, either anteriorly or posteriorly, although 

 a secondary migration might occur. This seems to have 

 been the case in some of the Chilopods, notably the Geo- 

 philidae. We would here hold to the opinion that the 

 spiracular openings have developed from numerous ir- 

 regularly disposed integumental glands of the Annelids, 

 as suggested, I believe, by von Kennel, and that the reduc- 

 tion and subsequent segmental arrangement parallels that 

 which has taken place and is still exhibited by existing 

 forms of the Onychophorids. 



The development of the transverse segmentation in the 

 parapodium to form the boundaries between the epister- 

 num-epimeron and the coxon-meron, as well as the coxon 

 and trochanter, etc., would be correlated with the increas- 

 ing chitinization of the integument and the need of me- 

 chanical assistance from the walking appendages, by the 

 individual. Such seems to have been the history of seg- 

 mentation among the Vertebrates, Echinoderms, Molluscs, 

 etc., both in the primary and the secondary axes of the 

 body. In other words, the need of pronounced articula- 

 tory surfaces is correlated with the development of firm 

 unyielding areas, such as bone, chitin, etc. 



The large acicular setae of the neuropodium, often 

 biuncinate distally, furnishes a part that may have readily 

 become transformed into the tarsal claws. Some evi- 

 dence for such a change is afforded by one of the fossil 

 Polychaetes mentioned later. 



Two forms of extinct Polychaete Annelids found by 

 Walcott in the Burgess Shales of the Middle Cambrian 

 Period near Field, British Columbia, are of much interest 

 in connection with the parapodial theory of insect evolu- 

 tion here presented. The specimen to which the name 

 Worfheuella camhria Walcott was applied in the paper 

 by Walcott (1911) is represented by a single individual 

 about 60 mm. in length, having some forty-six segments. 

 Two striking characteristics are observable, one in the 

 much elongated and apparently bilobed parapodium and 

 the other in the division of the segment into two sec- 

 ondary annular areas, as observed dorsally. The eyes and 



