HAMAKER: NERVOUS SYSTEM OF NEREIS VIRENS. 101 
third the diameter of a lateral connective, to the smallest, which how- 
ever are large enough to enable one to distinguish the circular outline of 
the sheath and its contents. 
There are three giant fibres, one in each connective. Those in the 
lateral connectives are much larger than the median one. 
On the median side of each of the paired connectives, close beneath 
the median connective, there is another very large fibre which, in some 
regions of the body, is but little smaller than the median giant fibre 
(Plate 5, Fig. 31). These fibres, which I shall call set A, also stain very 
lightly, but they show no traces of a network. 
The numerous fibres which constitute the remaining portions of the 
connectives stain more deeply. Most of them show no differentiation, 
but frequently the larger ones are more intensely stained in the centre 
than at the periphery. 
In longitudinal sections of the connectives (Plate 3, Fig. 26), the 
fibres appear as parallel bands separated by crinkled lines, — the fibre 
sheaths folded by a slight longitudinal contraction of the animal at the 
time of fixation. Many of the larger fibres, excepting set A, often show 
a darker central band corresponding to the darker centre of the trans- 
verse section. A few nuclei are scattered among the fibres of the 
connectives. 
Transverse sections through the ganglia of the ventral chain present a 
single central filrous mass bordered ventrally and laterally by ganglionic 
cells. Bundles of neuroglia fibres pierce the central mass at intervals 
along the median plane, and divide the ganglion into symmetrical halves. 
The greater part of the fibrous mass consists of longitudinal fibres, but 
there are many fibres which traverse the ganglion in other directions. 
The cells of the ventral ganglia do not vary as much in size, form, and 
structure as do those of the brain ; however, besides the uniformly gran- 
ular ones of various sizes and shapes (Plate 2, Figs. 13, 14, A), corre- 
sponding to those of class six in the brain, there are some cells (Fig. 
14, B) which stain very lightly, and the cytoplasm of which is homo- 
geneous with the exception of a few coarse granules of very limited dis- 
tribution. There are only a few pairs of these cells in each ganglion ; 
one of the pairs belongs to the fibres of set A, and these are among the 
larger cells of the ganglion. 
The coarse irregular granules of the cells last described occupy the 
middle of the cell, where they are arranged in the form of a hollow 
sphere, at the centre of which there is a round deeply staining granule 
(Fig. 14, B). This structure is undoubtedly what has been described as 
