0)1 an Australian Land Nemertinc. 107 



stout commissure which runs beneath the proboscis sheath 

 and above the oesopliagus and which we may call the ventral 

 commissure (Fig. 6, v. c.) The right and left dorsal lobes 

 are similarly connected by a slenderer commissure — the dorsal 

 commissure (Fig. G, d. c.) — which runs above the proboscis 

 sheath. In this way a complete ring is formed around the 

 proboscis sheath. The two ventral ganglia are continued 

 posteriorly into the lateral nerve cords (Figs. 2, 8, 24-, 25, n. c.) 

 These lie one on each side of the ventral aspect of the body, 

 within the layer of longitudinal muscles (Fig. 8) ; they run 

 straight to the posterior end of the body, where they unite 

 together above the intestine just in front of the anus. 



Various nerves are, of course, given off from the central 

 nervous system thus constituted, but these I have not 

 attempted to work out in detail and, indeed, to do so would, 

 owing to the minute size of the animal, be a very difficult 

 matter. The most conspicuous of these nerves are those 

 which come off from the antero-ventral aspects of the dorsal 

 lobes of the cerebral ganglia (Figs. 4, 5, n.) It will be seen 

 from Figure 4 that a specially large trunk leaves the brain 

 just above the ganglion of the lateral organ, and divides into 

 a number of branches, some of which run antero-dorsally 

 and probably sujjply the eyes, while another runs straight to 

 the sac on the lateral organ and yet another runs backwards 

 and somewhat ventralwards and divides into two short 

 branches, whereof one runs ' to the posterior end of the 

 ganglion of the lateral organ and the other to the curious 

 (esophageal organ marked x. in the figures. 



The histological structure of the central nervous system 

 bears a marked resemblance to that of the same organs 

 in Geo pi ana,*' hut the small nerve-cells are more abundantly 

 develo[)ed and more definitely arranged. In the brain 

 they occur abundantly in the outer portion of each 

 lobe, leaving the interior free from their presence. In the 

 lateral nerve cords the nei've cells are arranged in a very 

 characteri.>stic manner, as already described by von Graff in 

 the case of Geonemertes chalicophora. They are aggregated 

 in two bands, one on the ventral aspect of the nerve cord 

 and one on the dorsal aspect, but above the dorsal band of 

 nerve cells there is a narrow band of fibrous tissue. This 

 characteristic arrangement of the nerve cells in the lateral 

 cords is best shown in Figs. 2 and 25, (ii. c.) 



* Cf. Dendy, " Anatomy of an Australian Laud Planariau," Traus. Eoyal 

 Soc, Victoria, 1889. 



