ON THE NERVOUS SYSTEM OF THE NEMATODA. 199 
the water vascular system which lies a short distance behind 
the nerve-ring. These are termed the ram communicantes. 
In connection with these nerves are numerous ganglion- 
cells, which are found either in the course of the fibres or 
may be regarded as the points of origin of the fibres. The 
submedian nerves are furnished with but few of those bodies. 
The ganglion-cells are either dipolar, as are those occurring 
in the course of the fibres, or unipolar. The lateral nerves 
possess many more fibres than the submedian. Their fibres 
do not arise from the central ring alone. Numerous ganglion- 
cells of various sizes lie on all sides of the ring, and which 
are also unipolar and bipolar. Some might be termed multi- 
polar, were it possible to determine that all the processes 
arising from them were really nerve-fibres. These collections 
of ganglia are termed ganglia lateralia. 
A large mass of the kind is found in the ventral line im- 
mediately behind the ring, and the cells composing it are, 
probably, most of them connected with the rami com- 
municantes. In these ganglia (ganglia mediana) two halves 
may be distinguished, separated from each other by the tissue 
of the ventral line. On each side of the ventral line are 
placed six isolated ganglion-cells, two of which lie one be- 
hind the other, near the ventral line, and three others usually 
in the middle of the ventral space. These are unipolar. 
Their processes pass forward, and enter the middle ventral 
ganglion. The sixth cell is usually situated near the lateral 
intermuscular space. It is bipolar, and sends one process 
towards the median ganglion, and the other towards the 
lateral space. These cells are termed the ganglia ventralia 
dispersa. 
In these latter may best be perceived the histological con- 
nection between the nerve-cells and fibres. Each cell presents 
a distinct nucleus and nucleolus. The nerve-fibres are of 
some width, and when divided exhibit an elliptical section. 
A distinct membrane may be perceived pretty clearly in the 
cells, but not in the fibres. The latter consist apparently of 
a homogeneous substance, resembling, when acted upon by 
chromic acid, coagulated albumen. The structure of the 
central ring is not so readily made out. In the fresh state 
it is so elastic as to contract into about half its circumference 
when separated from all its attachments. All that can be 
stated with certainty is, that the ring is enclosed in a tough 
and dense sheath, which also sends processes inwards into 
its substance. This sheath is finely striated; the striez 
appearing to depend partly on fine rugz, in part also upon 
distinct fibres. On the exterior it presents no indication of 
VOL, I1I.—NEW SER. 2 
