— 113 — 
are very often situated in one side of the cell, near the surrounding 
sheath (cf. fig. 44 & 45) and, not unusually, towards that side from 
which the nervous process issues (cf. fig. 43, 1). They are, thus, 
very frequently situated outside the mesial, deeply stained, part 
of the protoplasm (fig. 44 & 45). In the small cells they are 
generally situated in the centre of the cell, and are proportionally 
very large, being surrounded by a thin layer of protoplasm only. 
The processes of the ganglion cells. — The ganglion cells 
of the Nereidæ have generally a unipolar shape. Quite exeptionally, 
I beUeve to have observed, in sections, cells with multipolar shape; 
there was always, however, only a single process in each cell capable 
of being traced in its course into the central dotted substance. 
The other processes were very short, immediately tapering off ; 
they were directed peripherically, or laterally, (never towards the 
central mass) and were soon lost in the neuroglia. I could, however, 
never quite convince myself of the real existence of such processes, 
and it is only in a very few cases I believe to have seen them (fig. 
67). I think that it is the issuing of neuroglia-fibres from the sheath 
of the cells that has generally occasioned the descriptions of multi- 
polar cells, as such fibres can look very like real cell processes 
(cf. fig. 44). 
The processes, or, as I call them, nervous processes, passing to 
the central dotted mass, and of which each ganglion cell has only 
one, have a structure similar to that of the nerve-tubes. They are 
surrounded by a neuroglia-sheath, and their contents consist of 
primitive tubes. 
In other forms of Polychæta the ganglion cells have, so far as 
my investigations go, a structure similar, principally, to what is here 
described. 
The membranes env elop ing the ganglion cells are formed 
by the neuroglia. They generally consist of one, or of a few, layers 
only. In the small cells they are thin, but distinctly marked; in the 
large cells they are often thick and well developed (vide fig. 44, cm). 
Neuroglia-nuclei adhering to them do not occur very frequently. 
^) Dr. E. Kohde (1. c. 1886 p. 785) distinguishes between two types of 
ganglion cells in the central nervous system of the Aphroditidæ. »Die Ganglien- 
zellen der einen Art sind sehr schwach granulirt, deshalb von hellen Aussehen und 
meist ziemlich klein. Ihr Kern enthalt stets mehrere verschieden grosse Korperchen 
und tritt nach Farbungen in der durchsichtigen Ganglienzelle scharf hervor.« »Die 
Vetreter des zweiten Typus sind sehr grosse, kugelige Gebilde, welche durch eine 
sehr dunkele Granulirung sofort in die Augen fallen. Sie besitzen einen grossen, 
8 
