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DR. H. W. HUBRECHT. 
on the surface of which it is subject to further dichotomic 
division. To this nerve the author assigns the name of 
N. vaguSf a term already employed by Leydig for other In- 
vertebrateSj and recently misapplied by Semper (who was 
then unacquainted with the presence in Nemerteans of a 
nerve such as the one here mentioned) to the dorsal com- 
missure of the cerebral ganglia in Nemertines. 
A thin longitudinal nerve, originating from the dorsal 
commissure and situated medially and dorsally, is looked 
upon by the author as a special nerve for the proboscidian 
chamber (PL XXIII, fig. 1). 
The anal commissure, situated above the intestine men- 
tioned above, presents no further particulars, its high mor- 
phological interest depending on the fact of its causing 
the whole of the paired symmetrical central nervous system 
present throughout the whole length of the animal to be 
situated, together with all the three transverse commissures, 
above the alimentary canal. 
The system of peripheric nerves is not exhaustively treated 
of in the present paper ; the author’s investigations on this 
point being not yet terminated. Still, certain points which 
may eventually prove to be interesting are already noticed. 
Whereas in the Hoplonemertini where the lateral nerve- 
trunks are situated inside of the mpscular body wall, small 
pairs of nerves springing from those trunks placed meta- 
merically, and distributing themselves to the muscular coats 
of the body wall can easily be detected, no such transverse 
stems to the longitudinal trunks could be detected in the 
ScHizoNEMERTiNi. Only here the author found a cellular 
layer, which he holds to be a nervous layer, encircling the 
body in the way of a tunic, and situated in a free space be- 
tween the outer longitudinal and the circular muscular layers 
(PI. XXIII, fig. 12,). The cells of this layer are multipolar, 
connected together as a sort of network, and uninterruptedly 
passing into the ganglion cells ensheathing the longitudinal 
trunks. Further details on the structure and significance of 
this layer are postponed by the author to a future paper on 
this subject. 
