650 



GERARD A STIASN Y-WIJNHOFF 



the wall of the sheath in Pelagica took place in the same way. 

 Primary are the stages with two muscle-layers, as Chuniella, 

 &c. The first stages of interlacing are given in Armaueria and 

 Dinonemertes (Text-fig. 20). In these genera started the 

 penetration of the circular muscle^coat by the longitudinal 

 fibres, or vice versa ; but the longitudinal musculature has not 

 yet reached the outside. We see an interlaced inner wall, 

 a longitudinal middle coat, and outside of it a circular layer. 



Text-fig. 20. 



rkyacJl.bL. y 



Transverse section through the rhynchocoelomic cavity of Dino- 

 nemertes albert i (Brinkmann) (4, PI. vii, fig. 13). 



As Dinonemertes seems to be connected with Mergo-, Phallo-, 

 and Paradinonemertes and Armaueria with Pendonemertes, 

 I might rather solve the problem of these genera as the begin- 

 ning of the interlacing, which is completed in Protopelago-, 

 Ploto-, Pendo-. Crasso-, Plankto-, Mergo-, Phallo-, and Para- 

 dinonemertes. 



Pelagonemertes kept the more primitive stage in the proximal 

 part of the sheath, which fact seems to point to the hinder part 

 of the cavity as the place of origin of the interlacing. Biir- 

 geriella gives still a higher development that confirms these 



