244 
MR. NEWPORT ON THE NERVOUS AND CIRCULATORY SYSTEMS 
orders Chilopoda and Chilognatha, the great divisions of the Myriapoda, it exhibits 
two marked conditions. In the Chilopoda it has the form of a double cord connected 
by large ganglia in each segment, as in most of the Annelida, Crustacea, and Insecta ; 
but in the vermiform Chilognatha, which former researches * have proved to me are 
most nearly connected to the Annelida, the two parts of this double cord are so 
closely united laterally as to appear like a single cord, that gives off a multitude of 
small nervous trunks at its sides throughout its whole length, but without distinct 
ganglionic enlargements at their origin. The cord is, nevertheless, composed in 
each Order of two longitudinal portions, more or less closely approximated, and 
united at certain distances by ganglia. It is extended along the under surface of 
the body beneath the alimentary canal, and its ganglia correspond in number to the 
number of segments, in strict accordance with the character established by Cuvier 
in his definition of the subkingdom Articulata. 
In all the Articulata two modes of development are in operation in the same animal; 
first that of growth, or simple extension and enlargement of each individual part ; next 
that of aggregation of two or more parts to form particular divisions or regions of the 
body. This latter mode of development is carried to a greater extent in insects than 
in any other of the Invertebrata, and, as is well known, changes the animal from a 
simple, elongated, worm-like larva, furnished with many pairs of organs of locomo- 
tion, and composed of segments almost uniform in size and appearance, to an indi- 
vidual of a totally different character, with its body divided into three distinct re- 
gions, differing in size and appearance, and separated from each other, with the 
number of its organs of locomotion reduced, and those that remain greatly enlarged 
and altered. Some of these changes in the segments take place also in the Myria- 
poda, but are carried only to a very slight extent. The head is composed of several 
segments, either consolidated together like the head in true insects, as in the vege- 
table-feeding Chilognatha, or separated, and moveable on each other, to adapt them 
to the carnivorous habits of the species, as in the rapacious Chilopoda. In like 
manner each moveable division of the body is in reality composed of two distinct 
segments, originally separate, but anchylosed together at an early period of their 
formation. Each of these sub-segments ought, therefore, to possess its separate gan- 
glion, and this in reality is the case. The head is composed of the elements of at 
least four segments, and perhaps even of six ; and contains ganglia, placed two above * 
and two below the oesophagus, which give nerves to the antennae, to the eyes, to the 
maxillae, and to the mandibles. The two anchylosed portions of each moveable seg- 
ment of the body have, in like manner, their separate ganglia, as in the Polydesmidce, 
in which the ganglia remain distinct throughout life in the posterior segments, but 
have coalesced in the anterior, more especially in those which are nearest to the head. 
These unions are occasioned by a reduplication inwards of the tegument, as in the 
aggregation of segments in insects, but this is carried to so slight an extent in the 
* Op. cit., Part II. 1841. 
