STUDIES ON THE NERVOUS SYSTEM OF CRUSTACEA. 39 
of ganglion cells, pursues a perfectly straight course until it 
reaches Th. 111, where it gives off a branch, which passes out 
through the posterior root of that ganglion. After giving off 
this branch the fibre continues to Th. 11, where it turns and 
leaves the ganglion through the posterior root. In one or two 
preparations, another branch appeared to be given off from the 
fibre in Th. tv, and to pass through the posterior root of that 
ganglion, but I was never able to make myself quite sure of 
this point. 
From the preceding description and the figure (fig. 1), it will 
be seen therefore that the element T, Th. viir supplies fibres 
to three (possibly four) nerve-roots of different ganglia, namely, 
the anterior nerve-root of Th. vir1, the posterior root of Th. rv 
(probable), the posterior root of Th. 111, and the posterior root 
of Th. 11, and that all these fibres have their origin in a single 
cell. 
A corresponding element occurs also in Th. vir (fig. 1, T, 
Th. vit). The cell is similarly situated to that of Th. vii1, and 
a fibre passes almost immediately to the anterior root of 
Th. vir. A second fibre pursues a straight course forwards, 
keeping close to the corresponding fibre of Th. vii1, until it 
reaches Th. 111, where it gives off a branch to the posterior 
nerve-root of that ganglion. The fibre then continues to run. 
forwards, but its ultimate destination has not been satisfactorily 
determined. It appears to turn inwards in Th. 11. 
Mention may here be made of a fibre which stains in almost 
every preparation from the earliest stages onwards. It is 
inserted in fig. 1, T (a). The fibre appears to run longitudinally 
through the ganglionic cord from the level of Th. 11 to the 
posterior region of the brain, and to give off branches to two 
nerve-roots. One branch passes out through the posterior 
root of Th. 11, whilst the second leaves the brain by a small 
nerve which arises immediately anterior to the nerve which 
supplies Antenna 11. A few small fibres are given off to the 
neuropile of the brain at the angle which the latter branch 
makes with the longitudinal fibre. 
No cell has ever been seen to stain in connection with the 
