594 THE WONDERS OF GEOLOGY. Lect. VI. 



In examining the other divisions of the animal kingdom, 

 the presence of a nervous system, more or less developed 

 according to their respective intellectual and physical en- 

 dowments, may be detected. In those of the higher orders, 

 nervous filaments can be distinctly traced, from their origin 

 in the brain or spinal marrow, to their distribution in the 

 various parts to which they communicate sensation, and to 

 the organs to which they impart the influence necessary for 

 the performance of their several functions. But in pro- 

 portion as the systems of absorbing, secreting, and circu- 

 lating vessels, become less, a corresponding diminution 

 takes place in the nervous fibres, till at length both vessels 

 and nerves elude our finite observation, and we are left to 

 infer from analogy, that, since sensation depends upon the 

 presence of nerves, and the smallest animals evidently 

 possess sensation, a nervous system exists in the minutest 

 Monad which the highest power of the microscope enables 

 us to descry.* 



In the largest and most complicated vegetable organisms, 

 no traces of nerves are perceptible, nor of any substance 

 which can be considered as at all analogous in structure 

 or function : it is therefore concluded, that as vegetables are 

 destitute of nerves, they are likewise wanting in the faculty 

 we term sensation, f 



* Hence Budolph, the celebrated physiologist, terms those animals 

 in which no traces of nervine, or nervous matter, can be detected, the 

 Cryptoneura, or hidden nerved. 



f Although the definition here given is sufficient for our present 

 purpose, yet it is necessary to state, that in a more rigorous and philo- 

 sophical view of the subject, a line of demarcation between the vital 

 phenomena exhibited by animal and vegetable organisms cannot be 

 established. The possession of a stomach or digestive sac, and the 

 power of locomotion, formerly thought to be peculiar to animals, are 

 no longer regarded as such. Even the difference in the chemical pro- 

 cesses effected by plants and animals, — namely, the absorption of car- 

 bonic acid and the evolution of oxygen by the former, and the opposite 



