TRACHEATA 305 
of legs, enlarged nephridia; the remaining twelve are normal, 
and resemble one another. 
The nervous system consists of a pair of supra-oesophageal 
ganglia, united by circum-oesophageal commissures with two 
ventral cords. Anteriorly each supra-oesophageal ganglion is 
prolonged into a nerve, which runs to an antenna (Fig. 175). 
Several nerves run to the skin, and laterally the optic nerves 
arise, and supply the eyes. A pair of sympathetic nerves 
emerge posteriorly from the brain; they run back in the wall 
of the pharynx, and unite on the oesophagus; both in their 
origin and distribution they closely resemble the sympathetic 
nerves of Chaetopods. 
Posteriorly the supra-oesophageal ganglia are continuous 
with the circum-oesophageal commissures, which in their turn 
pass into the ventral nerve cords. These latter lie in the 
lateral division of the body-cavity, and are consequently 
separated by a wide interval, but, like the pedal nerves of the 
Isopleurous Gasteropods, they are connected by a number of 
transverse commissures, nine or ten in each segment, the first 
of these lying immediately behind the mouth. ‘There are 
seventeen ganglionic enlargements on the ventral cords, cor- 
responding with the seventeen pairs of legs, and the circum- 
oesophageal commissures bear two ganglionic swellings, which 
supply nerves to the jaws and oral papillae. The ganglion cells 
are not confined to the swellings, but are distributed all along 
the cord. ach ventral ganglion gives off two large nerves, 
which pass into the legs, and a number of smaller nerves, which 
pass to the body-wall, etc. 
One of the most interesting features of the nervous system 
of Peripatus is that the ventral nerve cords pass dorsally at 
the posterior end of the body, and fuse together above the 
anus (Fig. 175), like the united visceral and pedal commissures 
in Chaetoderma. 
The eyes lie at the base of the antennae; beneath them is 
an optic ganglion; in their minute structure they resemble 
the eyes of Chaetopods or Gasteropods rather than those of 
Arthropods. 
The female is larger than the male, but the only external 
structural difference is the existence of a small white papilla 
20 
