THE NEMERTINI 189 



system is represented in the Turbellaria by the intercellular 

 lacunae of the parenchyma. 



It is by no means certain what function the system performs 

 in Nemertines. It is so far removed from the surface of the 

 body and the surrounding medium, except in those cases in which 

 the cerebral organ impinges upon the lateral vessel, that respira- 

 tion seems out of the question. Even in the head, where the 

 vessels are dilated into capacious sinuses, these are below the 

 musculature of the body wall, except in the region of the mouth 

 (Cerebratulus, etc.), where they come up to the basement tissue ; 

 but in this case it has no respiratory pigment as far as we 

 know. Even if there is a certain amount of gaseous interchange 

 in this region it seems more probable that the " vascular system " 

 in the Nemertines serves rather as a " nutritive " (lymphatic) 

 system, for the vessels are placed close to the wall of the enteron, 

 and dissolved food material can readily diffuse into them. Further, 

 the excretory system is always in contact with the lateral vessel, 

 from which the excretory products are, no doubt, removed. It is 

 probable that the distension of the dilated vessels at the anterior 

 end serve also to give firmness to the head during burrowing. 



The excretory system, which was originally observed by Max 

 Schultze and figured by him, 1 is always paired, and usually of 

 limited extent, being confined to the region of the foregut (Fig. 

 XXVII. n), extending backwards in short species at the side of 

 the enteron ; and, in Linens lacteus, forwards beyond the mouth. 2 

 The system (see 35) consists essentially of a 

 longitudinal, horizontal canal, which opens ex- 

 ternally below the lateral nerve, through a short, 

 transverse duct (p). This is usually single, but 

 in Amphiporus, Valencinia longirostris, and Eupolia 

 curta (Fig. XXVII. 3) there is a number of ducts, 

 one behind the other, each opening by a pore. 

 The canal which is lined by a ciliated epithelium 

 runs alongside the lateral vessel, and gives origin 

 to a number of branches, generally of the same 

 diameter as itself. These are short in Proto- 

 nemertini, or longer in other cases, and may even 

 be branched in Metanemertini, where they are 

 wrapped round the blood-vessel. Each branch Fl - xxviu. 

 terminates in a multicellular dilatation, contain- A "^Cg 11 " ^ lterea 

 ing a "flame" (Fig. XXVIIL). These "end 

 bulbs " push the wall of the blood-vessel inwards ; but there is no 



1 Max Schultze, Beit. z. tfaturgesch. d. Turbdlarien, 1851. 



2 Montgomery has recently described a series of nephridia extending throughout 

 the length of the body in Stichostemma, each with from one to five ducts, Zool. 

 Jahrb. (Anat.\ x. 1897, p. 265. 



