90 FUNCTIONS OF THE BRAIN. 



internal organs ; but the brain, nervous cord, and visecra, 

 are all placed in a common cavity. 



In articulated animals, the nervous system is reduced to a 

 knotted cord, and the organs of sense are gradually cxtin- 

 guislied. The heart ceases in this department, and respira- 

 tion also, as carried on by a particular organ. 



In the radiated department the organs of circulation 

 finally disappear ; the heart having been before abolished. 

 The alimentary apparatus is reduced to a simple bag with 

 one opening. Finally, in the microscopic animalcules all 

 special organs are at an end, and the animated being ap- 

 pears to our senses a spot of mere jelly. 



Take any organ or system of organs, and the same pro- 

 gress from complication to simplicity will be apparent. 

 Let us observe the nervous system. In man and the mam- 

 malia this apparatus consists of a brain and spinal marrow, 

 securely lodged in bony cases of cerebral and spinal nerves ; 

 of the system of ganglia called the great sympathetic nerve, 

 and of the five external senses. In passing through the 

 ■mammalia, we observe the brain considerably reduced in 

 size ; still farther diminished, and altered in its figure and 

 component parts, in birds ; lessened again, and greatly sim- 

 plified, in reptiles and fishes. 



In the mollusca, this large apparatus is reduced to one or 

 more small ganglia, with a few slender nerves ; to which 

 are added, the rudiment of an ear in one instance only, and, 

 in some others, imperfect and almost doubtful organs of 

 vision. 



In articulated animals, there is merely a straight cord with 

 a few branches ; in some of the more complicated radiated 

 animals, a few almost doubtful nervous branches ; and be- 

 low them nothing — neither brain, ganglia, nerves, nor or- 

 gans of sense. 



But there would be little inducement to compare together 

 the various animal structures, to follow any apparatus 

 through the whole animal series, unless the structure were 

 a measure and criterion of the function. Just in the same 

 proportion as organization is reduced, life is reduced ; 



