Different Animals, Gc. 485 
substance less and less concentrated, till it be- 
comes at length imperceptible and equally dis- 
tributed amongst all the parts of the most simple 
animals. 
The number of senses in this division is less 
than in the animals, that have vertebre. Sight 
is wanting in some of them; hearing in a greater 
number: But the remaining senses, especially 
feeling, appear to be never wanting.t Have 
these animals any sense, which is not possessed 
by those of the former division ? Some inge- 
nious physiologists think this probable. 
I shall in the next place mention a few of the 
pheenomena, or, as they are usually termed, Jaws 
of the nervous system, relative to sensation and 
voluntary motion in different animals. 
1. a. In man and other animals, belonging to 
the higher classes, when naturally formed, no 
sensation is excited by an impression, made upon 
any part of the body, if the nerves, distributed 
to that particular part, be divided, tied, or ~ 
so strong y compressed in any part of their course 
as to destroy the communication betwixt it and 
the brain, or spinal marrow. Henceit is proved, 
that neither the termination of the nerve, nor 
any part of it below its connection with the 
brain, or spinal marrow, is the seat of sensation. , 
+ Cuvier Anat, Comp. T. I. p. 37. 
