Although  the  power  of  receiying  obscure  im^
pressions  from  the  contact  of  external  bodies,
and  <^  perceiving  variations  of  temperature^  is
probably  possessed  by  all  animals,  a  smikll  num-
ber only  are  provided  with  organs  specially
appropriated  for  conveying  the  more  delicate
sensations  of  touch.  The  greater  part  of  the
surface  of  the  body  in  the  testaceous  MoUusca  is
protected  by  a  hard  and  insensible,  covering  of
shell.  The  int^uments  of  Insects,  especially
those  of  the  Coleoptera,  are  in  general  too  rigid
to  receive  any  fine  impressions  from  the  bodies
which  may  come  in  contact  with  them  ;  and  the
same  observation  applies,  with  even  greatei:  force,
to  the  Crustacea.  The  scales  of  Fishes,  and  of
Reptiles,  the  solid  encasements  of  the  Chelonia,
the  plumage  of  Birds,  the  dense  coating  of  the
Armadillo,  the  thick  hides  of  the  Rhinoceros,
and  other  Pachydermata,  are  evidently  incom*
patible  with  any  delicacy  of  touch.  This  nicer
faculty  of  discrimination  can  be  enjoyed  only
by  animals  having  a  soft  and  flexible  int^u-
ment,  such  as  all  the  naked  Zoophytes,  Worms,
and  MoUusca,  among  the  lower  orders,  and  Ser-
pents, among  the  higher.  The  flexibility  of  the
body  or  limbs  is  another  condition  which  is  ex-
tremely necessary  towards  procuring  extensive
and  correct  notions  of  the  relative  positions  of
external  objects.     It  is  essential  therefore  that


Eweinstrumeots  which  are  more  particiititrly
intended  as  organs  of  touch,  should  possess  this
property.
