coe: nemerteans of west and northwest coasts. 



35 



The muscular walls consist of an outer and an inner layer of cir- 

 cular muscles, between which is a much thicker layer of longitudinal 

 fibers (Text-fig. 10). The inner circular layer disappears posteriorly. 

 The middle chamber is constricted off from both anterior and pos- 

 terior chambers by strong sphincters of circular fibers. 



The proboscis is provided with a considerable number of distinct 

 nerves which are situated at equal intervals near the periphery of the 

 longitudinal muscles (Text-fig. 10). In Tetrastemma there are 

 usually 10 such nerves, in Amphiporus 10 to 20 or more, while in 



Fig. 11.— Paraneinertes califormca. Transverse section of proboscis tlirougli 

 basis of central stylet, showing the six pouches of accessory stylets symmetri- 

 cally arranged between outer and inner longitudinal muscular layers {obn and 

 ilm). Space between stylet pouches closely jjacked with large gland cells (gl) 

 filled with deeply staining secretion. Section of basis of central stylet (n) in 

 center of proboscis, surrounded by the radially disposed bundles of inner longi- 

 tudinal muscles. To the right of this a section of the duct (x) leading from mid- 

 dle to anterior chamber of proboscis. 



Drepanophorus there are 14 to 30 or more, the number being 

 fairly, although not absolutely, constant in each species. These are 

 described on page 53. 



It is in the thick muscular septum between the anterior and 

 middle chambers that the specialized armatm-e is situated (Text-figs. 

 7, 9, 11) . An extremely narrow canal leads through this septum and 

 connects the anterior with the middle chamber. In Amphiporus the 

 septum is comparatively thin (PI. 18, fig. 115), while in Emplec- 

 TONEMA (PI. 17, fig. 107) it is a number of times as thick as the 



