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points where the spinal nerves are given off. The cord 
gives off a pair of nerves situated in each inter-annular 
groove, and lying below the circular muscles, and in each 
chetigerous annulus either a pair of stout nerves or two 
bundles (right and left) of two to four nerves, which run 
outwards towards the parapodia, supplying the circular 
and longitudinal muscles between which they lie (fig, 55). 
In transverse section the cord is usually oval in shape, 
being flattened from above downwards. The cells are 
arranged on the ventral and ventro-lateral faces of the 
fibrous part of the cord. The entire cord is invested by a 
thin sheath of neurilemma, and the fibrous part of the 
cord is partially sub-divided into two by a median vertical 
sheet of neuroglia (fig. 54), 
The ganglion cells are chiefly unipolar, and are small 
and sub-equal, though here and there are larger cells, 
generally in the neighbourhood of the giant cells. 
The Giant Cells and Giant Fibres.—These cells are 
much larger nerve cells, placed at segmental intervals along 
the cord (fig. 52). There are no giant cells in the brain or 
cesophageal connectives; the first one occurs just behind 
the point of union of the connectives near the level of the 
groove between the third and fourth chetigerous annul. 
This cell belongs to the achztous segment (composed of 
the third and fourth annuli) immediately following the 
peristomium. The next cell is found in the annulus 
behind the first chetigerous annulus, and the cells in 
most of the other segments are found in a corresponding 
position, but they may be a little anterior or posterior to 
this level. The cells are, therefore, situated close to the 
posterior limit of each segment. In many of the segments 
only a single giant cell is present, but in about one-third 
or one-half of the segments two cells are found near 
together, one in front of the other. They are present in 
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