184 WILLIAM BLAXLAND BENHAM. 
system. There is no concentration to form a ganglion any- 
where. The chief part of the nervous system lies ventrally. 
Caldwell (4) describes a longitudinal nerve passing for some 
distance along the left side of the animal and a tube imme- 
diately below this nerve. 
As far as I can gather from the description given by McIntosh 
(19), he also observed a longitudinal nerve, but his description 
is rather vague, and I am not sure that I understand it. 
At first I completely overlooked the subneural “ tube ;” or 
rather I mistook it for a space between the epidermal cells. Mr. 
Caldwell, however, was good enough to point it out to me, and 
then I discovered that there are two such tubes, one on each 
side of the body (fig. 18). Hach starts from the level of the 
nerve-band, and runs along the body wall, close to the attach- 
ment of the lateral mesentery. Its structure appears to be as 
follows : a space between the epidermal cells is occupied by 
rather large cells, with processes passing to the wall of the 
tube (fig. 19); or perhaps this appearance is due to shrinkage 
of the semi-fluid contents of the tube (cf. giant-fibres of Earth- 
worms). I was unable to make out any punctated substance 
which might be a nerve, but this might readily be overlooked if 
the specimens were not very well preserved. What the meaning 
or what is the nature of the tubes I am quite unable to say. 
The epidermal cells overlying the nerve-band are very long 
columnar cells, with oval nuclei; pigment granules are present 
in amore or less definite arrangement, and the bases of the 
cells are branched. Between the branches are placed one or 
two layers of small nerve-cells with rounded nuclei (fig. 16). 
The nerve-band is modified over two small areas, viz. along 
that part of its course where it passes the nephridial ridge on 
each side (figs. 15, N.', 23, p.). 
Here the epidermal cells are somewhat shorter than over 
the rest of the nerve-band; and the nerve-cells are in four or 
five layers, more or less arranged in rows (fig. 17). The 
granular layer is also rather deeper here than elsewhere. The 
structure of this region recalls a sense organ; though it is not 
+ «Proc. Roy. Soc.,’ xxxiv, 1883. 
