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SECT. II.] CONSTITUTION OF THE NERVOUS SYSTEM. 387 



are clearly proved to be true animals by Spallanzani, who says: 

 " I am much more inclined to look upon them as true animals, 

 rather than as being solely vital and irritable, and I think my 

 opinion well founded, because I find in them that union of 

 qualities, which constitute (as I have previously stated) the cha- 

 racteristics of a true animal nature. I have already had occasion 

 to state some of those qualities in my Essay, and I include amoug 

 them the power of avoiding any obstacles, or individuals of their 

 own kind, that they may meet with ; of suddenly changing their 

 course and taking the opposite direction ; of passing suddenly 

 from movement to rest, without any apparent external shock. 

 I spoke of their darting towards particles in the infusions, of 

 the property they possess of turning incessantly upon them- 

 selves, of going contrary to the course of the fluid, of going to 

 the spots where a little moisture is left, and collecting there in 

 numbers, when the infusion has been dried up.^^ Erom these 

 and other facts advanced by the author, it is manifest that these 

 infusory animalcules feel, and have volition, and possess the cha- 

 racter of the true animal ; consequently, they are endowed with 

 a sentient and volitional principle, however destitute they may 

 be of a nervous system. 



Such being the facts, it follows that a nervous system is not 

 present in all animals, but that many insects have not cerebra, 

 and that infusory animals and creatures much larger than these, 

 are destitute of brain and nerves. But because these creatures 

 feel and move voluntarily like other animals, we must not con- 

 clude that the nervous system in man and many other animals, 

 is not the immediate instrument of sensation and animal motion. 

 Man and other animals endowed with that system, feel and 

 move by means of that system, nor, their organism being such 

 as it is, would sensation and motion be possible without nerves. 

 Insects, that have no cerebra naturally, are nevertheless en- 

 dowed with nerves, and perform their functions by means of 

 nerves only, and by the vis nervosa contained in them, which 

 exists without a brain ; and by this vis nervosa the acephalous 

 foetus lives in utero, and when born gives no slight signs of life. 

 Polypes, zoophytes, and other infusory animalcules that have 

 neither brain nor nerves, feel and move without a nervous 

 system, because the Author of Nature appears to have endowed 

 the pulp of which their bodies are composed with the facidty 



