chap, xii.] NER vo us Svs TEM OF PER IP A rus. 



401 



The ventral nerve cords are widely separated from one 

 another, but are 

 connected together 

 by a large number 

 of commissures (co 1 ), 

 of which there are 

 from nine to ten for 

 each segment of the 

 body. From the 

 outer borders of the 

 cords nerve fibres are 

 given off to all parts 

 of the body, the 

 whole of which is 

 consequently sur- 

 rounded by the ner- 

 vous system ; and we 

 have here, therefore, 

 what is essentially a 

 plexiform arrange- 

 ment, but one which 

 has, so to speak, be- 

 come regulated. A 

 further advance is to 

 be found in the fact, 

 that while the cords 



are everywhere CO- Fig. 172. Anterior portion of the central 



, T J ,. Nervous System of Peripaius, show- 



vered by ganglion in? the Anterior Cerebral Ganglia, 



Cells On their ventral wit j * he .,J; ateral Nerve Cords con- 



nected with one another by numerous 

 commissures (co). (After Balfour.) 



E, Eye ; atn, antennary nerve ; co i, first com- 

 missure: or??, nerves for the mouth ; org, 

 oral ganglion; pn, pedal nerves; ft/', 

 first ganglionic enlargement for tlie 

 pedal nerves. 



surface, the ganglia 

 are more especially 

 numerous at one 

 point in every seg- 

 ment of the bodv, 



n > 



where they form such an enlargement as that marked 

 ' in Fig. 172. 



Proneomenia may be taken as the simplest type of 

 A A 16 



