0,62 LECTURE VI. 



of animals, when they are sensible of light, 

 sound, odour, and touch, the upper gan- 

 glion which surrounds the oesophagus must 

 be considered as the brain, and from this, 

 nerves may be traced to the eyes, antennae, 

 and feelers. Mr. Astley Cooper tells me, 

 if the longitudinal nerve be divided in the 

 earth-worm, it can no longer regulate its 

 motions. When a worm is divided, each 

 part moves and crawls by its own powers, 

 but if the longitudinal nerve be divided, 

 when the worm is entire, the motions of 

 either end so counteract each other, that 

 the animal cannot crawl, which shows that 

 the volition of the worm proceeds from 

 its brain, and cannot operate on the parts 

 beyond the divided nerve. 



In insects and Crustacea, the nervous 

 system is similar to that of worms. 



In molusca, there is no longitudinal 

 source of nerves analogous to the medulla 

 spinalis. There is an upper ganglion, si- 

 milar to that considered as the brain in 

 the animals just mentioned, and a lower 



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