THE NEMERTINI 



181 



ring, thus formed, consists of nerve fibres wrapped round by gang- 

 lion cells. As in the case of all the Coelomocoela, except Echino- 



FIG. XVIII. 



Portions of transverse sections to illustrate the position of the lateral nerve stem in relation 

 to the muscular coats (after Biirger, more or less altered). 1, Carinina, a Protonemertine; 2, 

 Cephalothrix, a Mesonemertine ; 3, Amphiporus, a Metanemertine. a, epidermis ; b, basement 

 tissue ; c, circular muscles ; d, longitudinal muscles ; e, lateral nerve stem ; /, peripheral nerve 

 sheet ; i, enteron ; j, dorsal nerve ; p, lateral blood-vessel ; s, proboscis sheath or wall of the 

 rhynchocoel ; the proboscis is omitted ; t, dorsal blood-vessel ; v, parenchyma ; w, rhynchocoel ; 

 y, gonad ; y 1 , position of genital pore. 



derms, the anterior end of the system has come to be of greater 

 importance than the rest ; here each lateral stem thickens to form 

 a ganglion, to which is added a dorsal ganglion, closely connected 



