TR ACHE ATA 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. Each 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 



