300 
MR. NEWPORT ON THE NERVOUS AND CIRCULATORY SYSTEMS 
be shown from the manner in which they bound the posterior roots of the nerves, 
their influence can only be regarded as reflex, and not as voluntary or sensitive. Con- 
sequently, they tend to explain the cause of movements of parts on the same side of 
the body, excited by irritation of the nervous fibres connected with those parts in 
distant segments, in accordance with the theory of the reflex movements, as promul- 
gated by Dr. Marshall Hall. The uniform size of the nervous cord, into the struc- 
ture of which these fibres enter, in the interspaces between the ganglia, is a further 
reason for inferring their separate existence from those of the longitudinal series, 
which are traceable to the brain ; although they exhibit no structural differences 
from those series, and their separate existence is not distinctly marked, excepting 
where they bound the posterior surface of each nerve and ganglion, while passing 
inwards to form part of the cord. In other respects they closely resemble the fibres 
of the inferior longitudinal series, to which they are approximated. It is on account 
of the separate additions of these fibres to the cord, in the interspaces between the 
ganglia, that I have designated them fibres of reinforcement of the cord. According 
to these views, eacli nerve is formed of four sets of fibres, two of which, derived from 
the primary structures of the cord, the ganglionic and the aganglionic, which are 
traceable to the brain, are supposed to minister to volition and sensation : the other 
two, the fibres of reflected action, are the commissural, which communicate with those 
on the opposite side of the body, and those of reinforcement, which, independent of the 
brain, connect distant parts on the same side of the body. The ganglia of the cord 
are regarded not only as analogous, anatomically, to the enlarged portions of the cord 
in Vertebrata, but physiologically as centres of reflexion, agreeably to the views of 
Dr. Carpenter; and they also possess a still more important character and function 
in the nervous system, that of being the centres of growth and nutrition to the cord 
and nerves, the nuclei contained in them being perhaps the sources of supply and 
nourishment. This is shown from the fact that, in these parts, the fibres of the cord 
are softer and larger than in the rest of their course ; and are elongated during the 
growth of the body, and the development of new segments ; as is seen in the Polydes- 
midce and GeophUidce, families from the two divisions of Myriapoda. These additional 
facts fully accord with the already ascertained mode of development by extension, or 
simple growth of the segments. 
2. The examination of the circulatory system has afforded many facts, which appear 
equally new and important. In the whole of the Myriapoda and Arachnida a distinct 
circulation of the blood is carried on in vessels ; and such also is the case in insects 
and other Artie (data. These structures are less perfect in the earliest condition or 
larva state of the animal in each of these classes, in which many of the structures are 
still in the course of formation, more especially in those species which undergo a true 
metamorphosis, as in insects. A distinct system of arterial and venous structures 
exists in the Myriapoda and Arachnida. The first of these are in the original course 
of the fluids from the central organ, in the formation of the embryo. The systemic 
