STUDIES ON THE NERVOUS SYSTEM OF CRUSTACEA. 469 
one or at most two fibres are stained upon the same side of 
the cord that it is possible to trace them with certainty through 
their whole course. This, however, does not apply to the giant 
fibres (A (a) Br), which can always be easily recognised. 
A (b) Br.—This element starts with a cell of moderate size 
on the ventral surface of the brain immediately anterior to the 
large cell of the giant fibre (A (a) Br). The fibre passes first 
forwards and upwards, giving off numerous branches to the 
auterior lobes of the brain on both sides, and then backwards 
through the brain and down the ganglionic cord of the same side 
to the sixth abdominal ganglion. It give off collateral branches 
to the neuropile of the ganglia through which it passes. 
A (b) Th. I1I1.—The cell of this element lies on the inner 
ventral border of the lateral mass of ganglion cells of Th. III. 
The fibre runs forwards and inwards, and then forwards and 
outwards to Th. II. After giving off a branch which enters Th. I 
it turns downwards on the same side of the cord, sending off a 
stout branch in Th. III, and has been traced to the end of the 
thorax. It gives off collateral branches during its whole course. 
A (b) Th. I1V.—The cell lies in the median ventral mass of 
ganglion cells, but it is difficult to decide whether it should be 
considered as belonging to Th. III or Th. IV. The fibre passes 
forwards and outwards toa point in Th. III, where it gives off 
a stout transverse arm, which runs to the neuropile of the 
opposite side and there bifurcates. The main fibre turns 
downwards, gives off a branch which runs forwards to Th. II, 
and then runs down the cord on the same side as that on which 
the cell is situated. It has been traced to the end of the 
thorax, and gives off numerous collateral branches. 
B. 
These elements are represented in fig. 3. In all cases 
similar elements exist upon both sides of the cord, although, 
for the sake of clearness, only one is sometimes inserted. 
The elements consist of fibres starting from a cell ina thoracic 
ganglion and running forwards to the brain. Of this group 
the following have stained : 
