254 
MR. NEWPORT ON THE NERVOUS AND CIRCULATORY SYSTEMS 
forms the next ganglion (4.) which gives nerves to the third pair of legs, the poste- 
rior of the two pairs of organs of the segment, the female outlets being the analogues 
of the first pair. In the male the organs are situated further backwards behind the 
seventh pair of legs. Posterior to the fourth segment of the female, and the seventh 
in the male, the cord is extended backwards nearly in a uniform manner throughout 
the remaining segments, as far as the thirty-second ganglion, when it becomes less 
uniform. In this first part of its course it forms two ganglia in each segment, as we 
have seen in the double segments of lulus. These ganglia are separated only by a 
short interspace of cord (fig. 10. d d), but there is more than twice the length of cord 
between the last ganglion of one segment (8.) and the first of that next beyond it (9.). 
In the interspaces between these ganglia the cord gives off a pair of nervous trunks 
(c), which are distributed to the muscles and sides of the segments ; and each gan- 
glion gives off a single pair of nerves to the organs of locomotion ( d ). The nerves 
from the anterior ganglion in each segment are always directed backwards into the 
first pair of legs, since the ganglion is situated a little anterior to the coxae, and is 
more elongated in form than the second ganglion, the nerves from which enter the 
legs in a more transverse direction. But in proceeding backwards along the cord 
the distance between the ganglia is gradually lessened, until in the posterior segments 
the ganglia are found to follow each other very closely, and almost to unite. So 
again in regard to the nerves. Those which, in the anterior part of the cord, are given 
from it at equal distances between the ganglia, are found nearer and nearer to the 
ganglion next behind, until they at length cease to come from the cord, but are 
derived directly from the ganglia, each of which then gives off two pairs of nerves, 
instead of the single pair to the legs, as in the anterior segments. But although the 
ganglia are thus closely collected together, this is not the result of aggregation in 
this part of the body, but is consequent on the non-completion of changes which 
take place in the formation of new ganglionic centres and nerves in this part of the 
cord, during the successive periodic formation and addition of new segments to the 
body in these animals, as I have heretofore shown in the Iulidse*. These formations 
always take place in all the Myriapoda between the penultimate and antepenulti- 
mate segments, and in that part of the cord the new ganglia are produced to those 
segments. This leads us to some important facts in reference to the means by which 
the nervous cord itself is developed by extension and elongation of its fibres during 
the growth of the whole body, and the development of the new segments ; and it 
shows that an elongation takes place in the longitudinal fibres of the cord in the new 
segments, and that ganglia are developed in its structure while commissural and 
lateral fibres of reinforcement are in the course of formation. But the distribution 
of the nerves from these ganglia, and the structure of the ganglia themselves, seem 
to lead us to the facts. In Polydesmus maculatus (fig. 9.), Nob., each of the six pos- 
terior ganglia gives off two pairs of nerves. In no instance in these posterior seg- 
* Philosophical Transactions, 1841, Part II. 
