OF MYRIAPODA AND MACROUROUS ARACHNIDA. 
255 
merits of the body do the nerves come directly from intervening - portions of cord, or 
from spaces between the ganglia. The anterior pair from each ganglion are always 
given to the sides of the segment, like the nerves from the intervening cords in the 
anterior segments ; and the posterior, to the legs. In the last-formed of these gan- 
glia (36.) the ganglion is very short, the nerves (c, d) being given off from it almost 
transversely ; and the whole corresponds to the diminutive extent of the posterior of 
these newly-formed and incomplete segments. The ganglion (35.) immediately pre- 
ceding this is larger, and is separated from the one next before it (34.) by a more 
constricted portion of cord ; and it gives off its anterior pair of nerves (c) in a dia- 
gonal direction forwards. So again the next ganglion (34.) is still more complete, 
corresponding to the greater length and more perfect condition of the segment, and 
is separated from its fellow (33.) anterior to it in the same segment, by a short por- 
tion of cord. These two ganglia still give off their anterior pair of nerves, but there 
are no nerves given off from the cord. The form of the ganglia is now changing, 
the anterior one is becoming elongated, and its anterior pair of nerves are given off 
from it in a direction more diagonally forwards and outwards. The length of cord 
between this ganglion, and that in the segment immediately before it, is now greatly 
increased, but still no nerves are yet given off from this portion of cord ; they remain 
in connexion with the ganglion on which they have been formed. The ganglion (32.), 
anterior to this elongated portion of cord, also gives off both pairs of nerves, but the 
first pair are now at the very front of the ganglion, and are directed still more for- 
wards, and appear as if exerting much traction upon it, while the ganglion is narrowed 
and greatly elongated, and seems as if it were about to separate. This separation 
between the nerve and ganglion actually takes place in the next segment, in which 
the ganglion gives off but one pair of nerves, while the anterior pair comes from the 
cord, in close approximation to the ganglion. In this way the interspace between the 
ganglia is increased from behind forwards in each segment, and is greater in propor- 
tion to its distance from the terminal ganglion. The cord is elongated in the ganglia, 
by extension, or growth longitudinally ; and those nerves, which are given to the sides 
of the segments, and to the respiratory structures, and which originally are formed 
on the ganglia, or in immediate connexion with them, are gradually separated from 
them, and are afterwards attached only to the interspaces of the cord, so that they 
are removed to a greater distance from the ganglia in proportion to the earlier deve- 
lopment and more complete state of the segment to which they belong. This elon- 
gation of the cord commences in the posterior ganglion, at the front of which, appa- 
rently by separation of part of its own structure, the new ganglion of each last-formed 
rudimentary segment is always produced. Hence the ganglia must be regarded as 
performing a most important office in the nervous system, that of being centres of 
growth and nutrition to the cord and nerves. The structure of the ganglia confirms 
these conclusions, and shows that not only are these parts centres in which the re- 
flected motions of the limbs are effected, but that they are even of more importance, 
