NATURAL HISTORY OF CREATION. 245 



as a means of providing for the independent existence 

 and the various relations of animals, each species being 

 furnished according to its special necessities, and the 

 demands of its various relations. The nervous system— 



the more comprehensive term for its organic apparatus 



is variously developed in difierent classes and species, 

 and also in difierent individuals, the volume or mass 

 bearing a general relation to the amount of power. 

 Passing over the humblest orders, where nervous appa- 

 ratus is so obscure as hardly to be traceable, we see it in 

 the nematoneura of Owen * in filaments and nuclei, the 

 mere rudiments of the system. In the articulata, it is 

 advanced to a double nervous cord, with ganglia or little 

 masses of nervous matter at frequent intervals, and fila- 

 ments branching out towards each side ; the ganglia near 

 the head being apparently those which send out nerves 

 to the organs of the senses ; and this arrangement is only 

 less symmetrical in the mollusca. Ascending to the ver- 

 tebrata, we find a spinal cord, with a brain at the upper 

 extremity, and numerous branching lines of nervous 

 tissue,t an organisation strikingly superior; yet here, 

 as in the general structure of animals, the great principle 

 of unity is observed. The brain of the vertebrata is 

 merely an expansion of the anterior pair of the ganglia 

 of the articulata, or these ganglia may be regarded as the 

 rudiment of a brain, the superior organ thus appearing 

 as only a farther development of the inferior. There are 

 many facts which tend to prove that the action of this 

 apparatus is of an electric nature, a modification of that 



* Including rotifora, entozoa, cchinodermata, &c. 



t The ray, which is considered tlie lowest in the scale of fishes, or 

 next to the crustaceans, gives the first faint representation of a brain 

 in certain scanty and medullary masses, which appear as merely 

 composed of enlarged origins of the nerves. 



