STUDIES ON THE NERVOUS SYSTEM OF CRUSTACKA. 37 
mass of ganglion cells of the ganglion, and is relatively large. 
From the cell the fibre passes forwards and slightly outwards 
to the centre of the neuropile, where after turning downwards 
it bifurcates, sending one branch out of the ganglion through 
the posterior root, whilst the other runs as a transverse fibre 
to the neuropile of the opposite side. The element has not 
stained in any other ganglion of the thorax, but as will be 
seen later, what is probably the same element occurs in the 
abdominal ganglia. 
The element O in Th. vit (fig. 1) also sends its fibre through 
the posterior nerve-root. The cell lies in the anterior portion 
of the central mass of ganglion cells and pursues the course 
indicated in the figure, giving off branches to the neuropile 
on the side only on which the cell lies. The element occurs 
on both sides of the ganglion Th. vir, but corresponding 
elements have never stained in any other ganglion. 
ELEMENTS BELONGING TO NEW TYPES.—The motor elements 
referred to in Part I, and those already noticed in the present 
paper, are all characterised by the fact that the fibre leaves 
the central nervous system through one of the roots of that 
ganglion in which the cell attached to it is situated. The 
portion of the element which lies within the central nervous 
system is therefore entirely confined to one ganglion. In the 
cases now to be described, whilst the cell lies in one ganglion 
the fibre passes out of the cord by the nerve-root of some 
other ganglion. 
The element Q, Th. vir, is an instance of this class. The 
cell lies in the anterior portion of the central mass of ganglion 
cells of Th. vir, gives off a fibre which runs outwards and 
then upwards to Th. v1, where it passes out by the posterior 
root of the ganglion. The fibre gives off a stout arborescent 
branch in Th. vir, and a straight transverse branch in Th. v1, 
which passes across to the opposite side of that ganglion. 
This pair of elements has only stained in Th. vi. 
Three pairs of elements having many of the characteristics 
of the above, but differing in detail, are found in Th. tv, v, 
