NEMERTEA ENOPLA 651 



views, as it is the most specialized genus of the Pelagica in 

 many respects. The distal part acquired an inner circular 

 layer, as the originally outer circular coat after the stage of 

 interlacing, shown still in the proximal part, lost its longitu- 

 dinal fibres which all lie outside of it. This is in accordance 

 with the other anatomical facts, that make us look for the 

 nearest relations of this aberrant genus among species with 

 a basket-like structure of the sheath ; proximally it is 

 basket-like in Biirgeriella too : the distal part has an inner 

 circular and an outer longitudinal layer. Compared with 

 Text -fig. 20 of Dinonemertes the position of the fibres is this, 

 that the whole circular muscle-coat traversed the longitudinal 

 one (in Dinonemertes only the inner parts) and so came to 

 lie inside. Other traces of an inner circular muscle-coat fail, 

 and as Biirgeriella evidently is a highly speciahzed genus 

 it would be rather incomprehensible why it should be the only 

 one that had beheld this primitive feature on B r i n k m a n n ' s 

 explanation of facts. 



The other support of B r i n k m a n n ' s theory of a third 

 muscle-layer of the w^all of the sheath is Protopelagonemertes, 

 in which genus the interlacing of fibres is already found in 

 the nerve-ring. How^ever, if we suppose, as I do, that the 

 interlacing starts in the hinder part of the cavity and goes on 

 from behind forwards, as shown in Biirgeriella and Pelago- 

 nemertes, every reason fails why the interlacing should stop 

 with the brain as the nerve-ring lies in the muscular septum. 

 Protopelagonemertes bears its name quite undeserved, as 

 Pelagonemertes seems not to be related to it and is also to 

 a certain extent more primitive. 



The result of this discussion is that the genus Chuniella, 

 which after, Brinkmann 's description must be one of the 

 most primitive genera if not the most primitive genus of the 

 Polystilifera, perhaps even of the Hoplonemertini, has a pro- 

 boscis with exactly the same muscular layers as all primitive 

 Anopla, Malacobdella, and some Monostilifera, and as SJ^b o g a - 

 nemertes weberi, the most primitive genus of the 

 Reptantia ; that also the wall of the sheath in this genus is 



