J. Johnstone 
389 
have the paired ganglionic masses connected together by means of three 
commissures—two anterior and paired, and one posterior and unpaired. 
Each of the four anterior ganglia is continued backwards in the form 
of a very short longitudinal connective. Almost immediately after 
springing from the anterior ganglia each of these connectives swells out 
so as to form four posterior ganglia and from each of these masses a 
nerve takes origin : the four nerves so formed are the posterior bothridial 
nerves: they run backwards and outwards to the postero-lateral parts 
of the bothridia. 
The longitudinal connectives are then continued backwards and the 
two on each side fuse together and are joined by another connective 
which proceeds from the lateral margins of the posterior commissure. 
The three connectives of each side now fused together form the lateral 
nerve cord and this passes posteriorly along the scolex. Presumably it 
runs backwards and is continuous throughout the strobila from segment 
to segment, though I have not been able to identify it with certainty 
in the sections of the proglottides. Just opposite to the posterior 
margins of the bothridia, but within the axial part of the scolex, this 
lateral nerve cord swells out again to form what appears to be a short 
columnar ganglion, and a stout nerve takes origin in this structure. 
The two nerves so formed—the proboscidial nerve trunks—run backwards 
and inwards toward the axis of the scolex and very soon bifurcate. The 
two branches of each side run posteriorly, still enclosed in the same 
sheath of parenchyma between the proboscis sheaths, and at the 
beginning of the proboscis bulbs they separate from each other. Along 
that part of the outer wall of the bulb which is nearest to the axis of 
the scolex there is a strip of tissue of very obscure nature, consisting of 
parenchymatous and large rounded cells. The proboscidial nerves apply 
themselves to these strips of tissue and presumably the fibres penetrate 
into the muscular wall of the bulbs. It is quite unknown in what 
manner the finer fibi'es of the nerves end in the muscle fibres of the bulb, 
and I have, as yet, no observations to make with regard to this point. 
Now so far there is little doubt as to the relations of the various 
parts of the central nervous system which we have been considering. 
But whenever we begin to examine more closely into the minute 
structure of the masses called “ ganglia ” and “ commissures ” we 
encounter difficulties. The ganglia ought obviously to contain nerve 
cells, unipolar or multipolar, and the commissural and connective tracts 
should consist of nerve fibres, or of the ramifications of the processes of 
nerve cells. But of nerve cells there is no trace in the so-called ganglia. 
