134 



WESLEY R. COE. 



The nerves take up a position in the midst of the longitudinal 

 muscular layer along the whole circumference of the proboscis 

 (Fig. 10). This position varies somewhat in the different forms, 

 but is generally about two thirds the distance from the inner to 

 the outer border of the longitudinal muscular layer. Here the 

 nerves branch out to form a thick plexus of connecting fibers and 

 send symmetrical branches radially both towards the periphery and 

 towards the glandular epithelium lining the central lumen (Fig. 

 10). 



ocm 



tarn 



FIG. 10. Transverse section of everted proboscis of Ciinconemertcs 

 gracilis Coe, with the 12 proboscidial nerves (/>) connected by a plexus 

 in the midst of the longitudinal muscular layer (/m) ; icm and ocm, inner 

 and outer circular musculatures ; bm, basement layer underlying the inner, 

 grandular epithelium ; re, extension of the rhynchocoel ; lined with en- 

 dothelium. 



About midway between each two proboscidial nerves in certain 

 species the plexus is condensed into a secondary nerve, com- 

 monly about half the diameter of one of the main nerves. There 

 is thus an equal number of primary and secondary nerves in such 

 species. In some forms it is difficult to distinguish the two sets 



