34 



ANATOMY OF THE CENTBAL NERVOUS SYSTEM. 



ground; new impulses are excited, which pass to still other ganglia; and in 

 this way the contractions maj' extend to include farther metameres; in 

 short, an irritation affecting one portion of the worm's body, provided there 



Fig. 12. — Several ganglia from the ventral cord of an earth-worm, — Lum- 

 iricus terrestris, — showing the elements for successive movement-combinations. 

 (After Eetzius.) 



is the necessary co-ordination of movements present, brings the whole 

 animal, in a purely reflex way, into motion, — crawling. Indeed, this crawl- 



