262 
THE TANGANYIKA PROBLEM. 
Natica lineata : they are present in the gills of Lillorina, 
but curiously enough they are not represented in Haller’s 
figure of the gill of Sigaretus neritoides (Lam.). 
The osphradium is lodged in a groove beneath the gill ; 
it is simple, and slightly but distinctly tending to become 
pectinated. At the outer extremity it is curiously bent 
downwards and back, exactly repeating in this the condition 
of the same organ in Sigaretus neritoides and Natica 
lineata as represented by Haller. 
The nervous apparatus of S. zonata is remarkable, the 
whole completely simulating in every detail that of Lamel- 
laria perspicua , as figured and described by Bouvier and 
Haller. 
The cerebral ganglia are united by a short but distinct 
commissure, and are almost completely fused with the 
pleural ganglia. The right pleural ganglion gives rise to a 
nerve cord which passes upwards and directly across the 
axis of the animal's body. It almost immediately expands 
into a ganglionic mass, which represents the supra-intestinal 
ganglion. 
This ganglion is in turn connected with the left pleural 
by the commissure. The nervous system is therefore com- 
pletely zygoneurous on the left. From the left pleural 
ganglion a nerve cord passes almost parallel to and below 
the supra-intestinal commissure to a ganglionic enlargement 
which represents the sub-intestinal ganglion on the right. 
This ganglion is in direct connection with the right pleural 
ganglion by short connective. The nervous system is 
therefore completely zygoneurous on both sides. All these 
details could be made out by dissection alone, but the 
animals were so small that, for confirmation, I resorted to 
sections. In all essential details the nervous system just 
described corresponds with that of Lamellaria. 
