LEE BARKER WALTON 163 



Verhoeff, present not only on the anterior margin of the 

 prothorax but also upon the mesothorax, metathorax and 

 abdominal segments in Campodea, Japyx, etc., and com- 

 parable with similar areas among the Chilopods, as in the 

 Geophilids, etc. 



It seems quite obvious that the areas termed "primary" 

 may all be developed from the Polychaete segment, and 

 that the correspondence between the parapodium and 

 the pleural area and basal parts of the leg in the Hexapods 

 indicates a definite relationship. With the parapodium 

 turning on its axis, as indicated in Fig. 2, the proximal 

 part coalescing with the pleural part of the segment and 

 the ventral branch becoming elongated and eventually 

 segmented as it attains a ventral position supporting the 

 body, there is, I feel certain, an explanation of the origin 

 of insects much more satisfactory than any of the theories 

 thus far advanced. 



It will be well to discuss somewhat more explicitly cer- 

 tain details in connection with the typical structure of 

 the segment among the insects which bear upon the solu- 

 tion of the problem. 



In the suggestion that the basal part of the parapodium 

 has fused with the lateral area of the segment to form the 

 episternum and epimeron, there is really nothing extra- 

 ordinary. A phyletic development of a similar nature 

 has taken place among other insects, and is particularly 

 noticeable in the family Dytiscidae of the Coleoptera 

 where the metacoxae have the form of expanded plates 

 immovably fused with the sternum. Furthermore, as 

 Haase (1889^) has pointed out, each abdominal sternite 

 in the insects represents a pair of coxae that have fused 

 with the sternum so that all trace of the sutural region is 

 lost in most forms. 



The division of the pleurum into two areas is not at all 

 confined to the thorax, as some would have us believe, but 

 is to be noted in head region as well as in the abdominal 

 region of many insects. Thus, as I have pointed out 

 (1913), the cardo at the base of the maxilla is composed 

 of two pieces which I there termed the endocardo and the 

 ectocardo on the basis of their apparent correspondence 



