40 WILLIAM A. HASWELL. 
These hollow striated muscular fibres are, as already men- 
tioned, radial in their arrangement. They are arranged in 
regular transverse (annular) rows in the wall of the cylindrical 
gizzard, their broad outer ends (which are hexagonal) fitting 
in closely together, the narrower inner ends also being in close 
contact. Through the middle, or nearly through the middle, 
of the basal ends of all the fibres of each row there runs a 
narrow fasciculus of non-striped muscle (fig. 17), which thus 
forms a loop round the outside of the cylindrical gizzard, the 
completeness of the loop, however, being interrupted along two 
longitudinal lines—the dorsal and ventral raphes—where the 
fibres of neighbouring loops interlace. The outer end of the 
central core of each striated muscular fibre, just internal to the 
corresponding loop of non-striated muscle, is occupied by a large 
ganglion-cell (figs. 17—20). This ganglion-cell is very clearly 
visible in the fresh state, owing to its containing numerous 
granules of ared pigment.!_ Hach cell contains a Jarge vesicular 
spherical or oval nucleus, or several, each nucleus having a single 
spherical nucleolus. The protoplasm of the cell sends out a 
large number of radiating processes, which penetrate between 
the bundles of fibrils, branching repeatedly, so as to give rise 
to a complex system of very fine threads. The processes thus 
given off from the ganglion-cell run partly parallel with the 
outer surface of the gizzard; but some also are given off from 
the inner aspect of the cell, and run obliquely inwards between 
the bundles of fibrils, or are continued directly inwards along 
the core. Of the latter series of processes there is usually one, 
or there may be two, in each fibre ; they branch again and again, 
and their branches seem to become lost among the threads of 
the network of the core, to be described presently. The sub- 
1 The same pigment occurs in many of the tissues of the worm—in the 
nerve-cord, the hypoderm, the epithelium of the alimentary canal and of the 
segmental organs, the ova and the mother-cells of the spermatozoa; ona 
spectroscopic examination it does not present the absorption bands character- 
istic of hemoglobin, and thus differs from the red pigment in the pharynx of 
Aphrodita (Ray Lankester, “ A Contribution to the Knowledge of Hemo- 
globin,” ‘ Proc. Roy. Soc.,’ xxi (1872), 
