168 THE SHORTER SCIENTIFIC PAPERS 



the appendages of the head leave no question as to the 

 Polychaete nature of the specimen, although, as Walcott 

 correctly suggests, it belongs to none of the existing 

 families of these annelids. 



If we attempt the reconstruction of a typical segment 

 of Worthenella on the basis of the available data, there 

 are two alternative hypotheses which one may consider. 

 The one appearing to me as the most consistent interpre- 

 tation is that of representing the parapodium turned 

 somewhat clockwise on its axis so that the lobular division 

 extending to the dorsal margin of the segment forms a 

 continuation of the boundary separating the secondary 

 annular areas. It is possible, of course, that the annular 

 groove is not related to the biramose division of the para- 

 podium. So far as the outline of the parapodia are con- 

 cerned, however, they are folded in such a manner that 

 the clockwise turning is indicated. The other interpreta- 

 tion is that the apparent segment represents a fusion of 

 two primitive segments, as in existing Diplopods, and that 

 each lobe is a distinct parapodium. One would not ex- 

 pect such a specialization, however, in an evolutionary 

 stage where the comparatively thin cuticula was quite 

 sufficient to take care of the contortions of the individual. 

 A distinct segmentation followed by segmental fusion 

 belongs to a later phyletic period. 



Another form found by Walcott which must also re- 

 ceive consideration in any discussion of the evolution of 

 the insects and the classes allied to the insects is Aysheaia 

 peduncnlata Walcott also from the Burgess Shales. The 

 parapodia possess terminal "hook-like and straight setae" 

 and closely resemble the ambulatory appendages of exist- 

 ing Onychophorids where the terminal claws have un- 

 doubtedly developed from similar hook-like setae. That 

 the tarsal claws of the insects have had a similar develop- 

 ment seems extremely probable, although a different line 

 of descent is indicated from that of Peripatus and its allies 

 where the appendage has developed from a simple and not 

 from a biramose parapodium. 



Among existing Polychaetes the relation of the various 

 areas of the parapodium to the pleurites in the appendage 



