APGr 



402 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



the Mollusca, but it is impor- 

 tant to note that along this 

 phylum we have persisting a 

 larger number of conditions 

 than are at present, at any 

 rate, known among the Ar- 

 thropoda. A reference to Fig. 

 ITS will show that, in Pro- 

 neornenia, there are, on either 

 side, two 1 cords which run 

 down the whole length of the 

 body, and both of which ter- 

 minate in a ganglionic swel- 

 ling ; the two inner cords are 

 seen to be Connected with one 

 another by commissural fibres, 

 and each of these with the edge 

 of the cord that lies outside 

 it j as these latter give off 

 peripheral nerves it follows 

 that here again we have a 

 plexus of nerve fibres distri- 

 buted through the body. In 

 the case of Proneomenia we 

 have ganglion cells not only 

 accompanying the nerve fibres 

 throughout the whole of their 

 length, -but they are also, as 

 they are in some of the com- 

 missures of Peripatus, found 

 on the commissures which con- 

 nect these cords with one an- 

 other. Here, then, we have 

 yet another instance of the 

 plexiform disposition of nerve 

 fibres, and the diffused condi- 

 tion of ganglionic cells in a 



.TPG 

 JVC 



Fig. 173. Diagram of the 

 Nervous System of Proneo- 

 menia. 



CX3, Cerebral ganglion ; sty, sub- 

 lingual gansrlla ; APG, PPG, PVO, 

 anterior pedal, posterior p -dal, 

 posterior lateral (visceral) 

 ganglia ; el, sublingual con- 

 nectives ; Cpc, cerebropedal 

 connectives ; pe, longitudinal 

 pedal nerve trunks ; la, longi- 

 tudinal lateral nerve trunks. 

 (After HubrechU 



