PHYLUM PLATYHELMINTHES 



'271 



commissures, dorsal and ventral, between which pass the proboscis 

 and its sheath. From the brain pass backwards a pair of thick 

 nerves which run throughout the length of the body ; usually 



a " P. 



long, ne 



long.ne 



l.bv 



FIG. 210. Diagrammatic transverse section of a Ntmerteaii (Cari,i<.Un). a, b, c. layer* <>t 

 body -wall ; c. t. connective tissue between body-wall and enteron ; I. br. lateral blood-vessels ; 

 ln,iii. nc. longitudinal nerve ; p. proboscis ; p. s. proboscis sheath. (After Hubreeht.) 



these are lateral in position, sometimes approximated dorsally, 

 sometimes ventrally. In the Nemerteans devoid of stylet there is 

 a nerve-plexus between the muscular layers. In the stylet-bearing 

 forms such a plexus is absent, but metamerically arranged branches 

 are given off by the nerve-cords ; these divide into smaller nerves. 



ncph 



medbfo 



FIG. 220. Anterior portion of a Nemertean ( Krepaimphorus), showing the -blood-vascular 



and excretory systems. Inf. hi. r. lateral !>1 1-vessels ; mv.l.U.'c. median blood-vessels: 



neph. nephridial (excretory) tubes. (After Oudemaiis.) 



for the supply of the various organs. Sometimes the lateral cords 

 unite behind above the anus. 



A remarkable apparatus connected with the nervous system is 

 the system of lateral organs. These consist of a pair of ciliated 

 tubes (Fig. 215, cil. gr.} opening externally at the sides of the head,, 



