646 GERARDA STIASNY-WIJNHOFF 



this is the case too, as in Siboganemertes and all Reptantia ; 

 but in Chuniella, Nectonemertes, Natonemertes, Para-, Pro-, 

 and Balaenanemertes no traces of interlacing of these fibres 

 are found, and the longitudinal layer lies next to the endothe- 

 lium exactly as in the Monostilifera (Text-fig. 17). Br ink- 

 ma nn considers this kind of rhynchocoelomic musculature 

 not as primitive, because the layers show another arrangement 

 at the place of insertion of the proboscis. We know, however, 

 from the Anopla that exactly in this part of the proboscidian 



Text-fig. 18. 



■rhyruJxi.Tnj 



Section through the rhynchocoelomic waU of Drepanophorus after 

 Burger (6, PI. xxiii, fig. 37). 



system the first traces of the new outer longitudinal layer appear, 

 when the middle part holds the older structure ; that here 

 other layers disappear first, that in other species fail absolutely 

 and in more primitive genera are present in all parts ; that 

 at this spot new constrictors and retractors can develop, that 

 in most species are unknown, to be short, that all changes 

 start in this part of the proboscidian system. When we remem- 

 ber, moreover, that this spot is the place where originally the 

 invagination of the whole system took place, that by the 

 development of the precerebral region, as will be discussed 

 later, the continuity with the body musculature was broken, 

 ' Muskelseptum, Riisselfixatoren ' originated, ' Seitenstamm- 

 muskeln ' developed ; that the inner circular muscle-layer 

 is and must be present in the rhynchocoelomic wall, but almost 

 disappeared in the body-wall ; that originally here the central 



