68 Instinct and Intelligence 



tion of nervous matter was effected, forming 

 an organ which we recognise as the animal's 

 brain. 



The body of a large earth-worm contains a 

 series of from 100 to 200 segments or somites, 



each of which is fur- 

 nished with four pairs of 

 bristles or chsetse mov- 

 able by muscles, and con- 

 stituting the animal's 

 chief locomotory organs. 

 An earth-worm's mouth 

 is situated on the under 

 surface of its head; at 

 the posterior extremity 

 of its body is a terminal 

 opening or anus. The 

 nervous system of these 

 worms consists of two 

 masses of nerve cells and fibres (ganglia) 

 situated just above the passage leading from the 

 animal's mouth to his stomach (Figs. 9 and 10). 

 These ganglia give rise to the nerves passing 

 forwards to the head and to. a ganglion situated 

 below the gullet, from whence a cord of 



FIG. 9. a, cerebral ganglia ; 

 b, mouth ; c, ventral nerve 

 tract ; d and e d f, respec- 

 tively marginal, dorsal, and 

 medio-dorsal nerve tracts. 



