NEMERTEA ENOPLA 



645 



armed Nemerteans. The other difficuhy was that the spot 

 where delammation took place seemed to be different m the 

 Enopla. For in the unarmed Nemertini the inner longitudinal 

 muscle-layer was split into two parts that enclose the rhyncho- 

 coelomic cavity, which is lined by an endothelium. However, 

 in the Hoplonemertini a circular muscle-layer lies between 

 the longitudinal fil)res and the endothelial lining of the pro- 

 boscis (Text-fig. 16). I then suggested that these circular 



Text-fig. 17. 



tKZ.ttx,. 



TCudj TTO . 



TVS.p 



Section through Emplectonema gracile after Burger 

 (6, PI. XV, fig. 27). 



fibres are a new acquisition and do not belong to the jjrimary 

 proboscis, as the proboscis sheath itself is built like that of the 

 Anopla (Text-fig. 17). Chuniella, one of the most primitive 

 Polystilifera, seems to prove this supposition, as the proboscis 

 has no circvilar muscles beneath the endothelium, and in 

 Monostilifera the genus Zygonemertes (19) shows the same 

 feature, as sections from South African species reveal. We 

 knew nothing then about Polystilifera with the exception of 

 the genus Drepanophorus, in which the wall of the rhyncho- 

 coelomic cavity consists of longitudinal and circular muscle- 

 fibres, that are interwoven (Text-fig. 18). In many Pelagica 



