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Chapter VIII. 



COMPARATIVE PHYSIOLOGY OF THE NERVOUS 



SYSTEM. 



§ 1 . Nervous Systems of Invertebrated Animals. 



Our knowledge of the exact uses and functions 

 of the various parts which compose the nervous 

 system, and especially of its central masses, is 

 unfortunately too scanty to enable us to discern 

 the correspondence, which undoubtedly exists, 

 between the variations in the functions and the 

 diversities in the organization. The rapid re- 

 view which I propose to take of the different 

 plans, according to which the nervous system is 

 constructed in the several classes of animals, 

 will show that these central masses are multi- 

 plied and developed in proportion as the facul- 

 ties of the animal embrace a wider range of 

 objects, and are carried to higher degrees of 

 excellence. 



In none of the lowest tribes of Zoophytes, 

 such as Sponges, Polypi, and ^leduscE, have any 

 traces of organs, bearing the least analogy to a 

 nervous system, been discovered ; not even in 



