OF MYRIAPODA AND MACROUROUS ARACHNIDA. 
247 
One of the most interesting circumstances connected with the development of the 
nervous system in lulus, is the relative size of the brain as compared with that of 
these ganglia of the viscera. In these inferior Myriapoda, in which the power of 
locomotion is distributed equally to every segment of the body, the brain itself 
forms but a small proportion of the whole nervous system, and the faculties of sense 
are less perfect than in insects; while the nerves of organic life, and their ganglia, 
are nearly equal in volume, as in lulus, to the whole brain, the organ of volition. 
The very reverse of this is the case in insects. In those in which the faculties of 
sense, more especially of vision and smell, and the power of voluntary motion are 
carried to their greatest extent, as in volant insects, — the gregarious Hymenoptera, 
Neuroptera, and Lepidoptera, — the volume of brain bears a much larger proportion 
to the rest of the nervous system, and the ganglia of organic life a smaller. This 
is more especially the case in the perfect insect, in which the volume of brain is not 
merely relatively, but actually increased in size during the changes from the larva to 
the perfect state, thus leading to the inference that the importance of the visceral 
nerves is gradually diminished in proportion as those of volition and active existence 
become augmented. 
Notwithstanding this inferiority of organization in the nervous system of lulus, 
the brain is inclosed in a proper covering, and is separated from the surrounding 
structures by a distinct membrane, but this is so delicate as to be detected only with 
some difficulty. It is completely inclosed in this structure, which also sends off pro- 
longations that form a covering for the oesophagus with its vessels and nerves. 
The nervous cord is extended from its commencement in the crura of the brain (g) 
and medulla oblongata, or first suboesophagcal ganglion ( h ) to the antepenultimate 
segment ot' the body, and is almost uniform in size throughout its whole length. It 
is slightly larger at its anterior, and smaller at its posterior extremity, than in the 
middle part of its course. In lulus terrestris it has ninety-six very minute ganglionic 
enlargements, situated entirely on the under surface of the cord, and so closely ap- 
proximated together as not to be observable, except on very close inspection. Each 
of these enlargements gives off two pairs of nerves, one of which, on the under sur- 
face, is given to the legs, and the other, on the lateral and superior surface, to the 
sides of the body ; so that the whole number of nervous trunks from the cord, in- 
cluding those from the medulla oblongata, is ninety-four pairs to the head and sides 
of the body, and ninety-two pairs to the legs, making in the whole one hundred and 
eighty-six pairs, or two hundred and seventy-two nervous trunks from the cord, 
exclusive of those which belong more immediately to the brain. In Spirostreptus 
(fig. 3.) the ganglia are even smaller and closer together than in lulus, but the cord 
is larger in proportion to the size of the nerves, the distribution of which is almost 
precisely the same as in lulus. Each enlargement of the cord (a) gives off at its 
upper and lateral surface a single nervous trunk ( b ), which passes outwards for some 
distance as a single nerve, but which in reality includes two distinct sets of nerves, 
