258 
MR. NEWPORT ON THE NERVOUS AND CIRCULATORY SYSTEMS 
in the posterior region of the body they are elongated, and somewhat oval. Treviranus 
has correctly described and delineated them as giving off each three pairs of nerves, but 
he has not identified these with the nerves of Scolopenclra, or of insects. It has been 
seen in lulus and Polydesmus that each moveable segment of the body is originally 
composed of two others that have become united, and that each of these contains a 
ganglion. In Polydesmus the ganglia of each segment are nearer together than those 
of two separate segments, and notwithstanding the manner in which the intervening 
cords are developed, there is a tendency in the ganglia to unite. In Geophilus each 
segment is also composed of two parts, but one of these is much smaller than the 
other, and is fast disappearing. Hence the ganglion in each of these segments may be 
regarded as formed of the elements of two ganglia. Three pairs of nerves are given 
off from this ganglion in close approximation, at its posterior lateral surface, in the 
posterior half of the cord, but these are separated from each other in the anterior, in a 
manner similar to what we have already seen in Polydesmus. The posterior pair of 
nerves from each ganglion (fig. 13.81. d) are supplied to the pair of feet. Immediately 
anterior to these, and coming as it were from the same origin, the proper muscular 
nerves passes outwards to the sides of the segment. These nerves, as is the case with 
the corresponding muscular nerves in the larvae of insects, pass on the outside of the 
longitudinal layers of muscles, between them and the diagonal muscles, to the sides 
and upper part of the segments, and thus are enabled to give off branches in their course 
to both layers. The third or anterior pair of nerves (c) are analogous to the respira- 
tory nerves of insects. They pass off from above the ganglion on the upper surface 
of the cord, and after crossing the longitudinal layer of muscles, on their inner side, to 
which they give filaments, are distributed to the spiracles and muscles connected with 
them. These nerves vary a little in their mode of passing off from the ganglia, owing to 
the changes which take place in the ganglia, as already seen in Polydesmus. They are 
composed of fibres derived, as in that genus, both from the ganglion and sides of the 
cord, and its superior tract, above which they are formed by the union of these with a 
series of commissural fibres. In the posterior part of the cord (81. 82.) these nerves pass 
off in the same trunk with, but immediately anterior to, the second or muscular pair, 
but in the middle of the cord they pass off more anteriorly (fig. 14. c), while in the 
anterior segments, in which all the ganglia are slightly enlarged and rounded (fig. 12.), 
they pass off directly from the front of the ganglion. This pair of nerves is of great 
interest in the anatomy of the nervous system, since these are the analogues of nerves 
which exist in the Crustacea and in Insects, and in the latter, as in Geophilus, they 
are always given to the organs of respiration. They have the same relations to the 
other nerves and layers of muscles in all, but in Geophilus they lie on the superior 
longitudinal tract of the cord, in actual contact with a ganglion, deriving part of their 
structure from the ganglion, from the fibres of reinforcement, and from the aganglionic 
tract ; and they also contain commissural fibres, precisely as in the respiratory nerves 
of insects. They exist in all the families of Chilopoda, but with this difference, that 
