EVOLUTION OF LIFE. 71 



the larvae and zoophytes, and that large and 

 intermediate class of beings which connect the 

 animal, with the vegetable, kingdom, although 

 there is a structure, of a nervous appearance, 

 which is expanded over the whole surface of the 

 body, the existence of a brain, as a distinct organ, 

 is not discernible. As we descend from the higher 

 to the lower orders, we shall find that the mag- 

 nitude of the brain progressively decreases from 

 the white, to the black, of the human species, 

 from bipeds to quadrupeds, from quadru- 

 peds to birds, from birds to fish, from fish to 

 insects, where all traces of the existence of 

 brains and nerves, as organs, separate and dis- 

 tinct, are altogether lost. The extensive power 

 in them, which the organs of- sense possess, is 

 more especially calculated to attain those ends 

 which, in the great scheme of providence, they 

 are destined to perform : the sense of want and 

 of appetite, which the organs suffer, constitutes 

 the impulse whence all their motives spring, and 

 to the relief and gratification of which, all their ( 

 actions are especially directed. It is the power 

 whence the impulse arises which may be called 

 instinct. It constitutes the principle, by the ' 

 energy of which,, certain organs are employed 

 to perform certain determinate actions, with a 

 view to certain ends or consequences ; they are , 

 impelled by natural and blind impulse, which 



