NEMERTEA ENOPLA 



665 



clear, and the presence of muscle-strands in the snout can be 

 understood also. The newly developed region could only 

 get some small outer layer of the musculature as the bulk of 

 the muscular coat is used by the formation of the proboscidian 

 system. So we find the greater part of the longitudinal muscula- 

 ture as the septum before the brain or as proboscidian muscles, 



Longitudinal section through the anterior region of Nee to- 

 ne mertes primitiva (Brinkmann) (4, PI. 12, fig. 13) to show 

 the total absence of a head and rhynchodaeum. The proboscis 

 is lost and the stomodaeum protrudes through the mouth. The 

 tip of the snout is indicated by a cross. 



and only a very thin layer of longitudinal fibres is seen to 

 accompany the epithelium and the few circular fibres under- 

 neath. That in this process of division of the musculature some 

 longitudinal fibres are found in the parenchyma of the snout, 

 that connect the musculature of body-wall, rhynchodaeum, 

 and septum seems to be quite natural. The aberrant structure 

 of the head of all Nemerteans as far as concerns the musculature 

 can only be understood in this way. 



