INTRODUCTION. 59 



It is evident that such characters must be de- 

 rived from the animal functions of sensation and 

 motion, for these not only constitute and create an 

 animal, but also by their greater or less capacity 

 may be said, in some measure, to establish the de- 

 gree of its animality. This position is confirmed by 

 observation, inasmuch as we find that the degrees 

 of development and complication of the animal 

 functions bear a true proportion with those of the 

 organs, which execute the mere vegetative functions 

 of life. 



Heat and the organs of circulation form a kind 

 of centre for the vegetative functions, as the brain 

 and the trunk of the nervous system do for the ani- 

 mal ones ; for as we trace the animal tribes, from 

 the superior to the inferior, we find these two sys- 

 tems grow gradually more imperfect in an equal 

 proportion, and finally disappear together. In ani- 

 mals the lowest in the scale, where the nerves are 

 no longer visible, the fibres also cease to be distinct, 

 and the organs of digestion are nothing more than 

 simple cavities in the homogeneous mass of the 

 body. In insects the vascular disappears even be- 

 fore the nervous system ; but, in general, the dis- 

 persion of the medullary masses is simultaneous 

 with that of the agents of muscular motion : a 

 spinal marrow, upon which a certain number of 

 knots, or ganglia, represent so many brains or 

 seats of sensation, corresponds with a body di- 

 vided into numerous rings, and supported upon 



