898 
ME.  C.  DE  MOEGAX  OX  THE  STEHCirEE  AXD 
While  no  doubt  the  hairs  have  other  and  mechanical  offices  to  fulfil,  it  Tvould  be 
difficult  to  suggest  any  use  besides  that  of  ministering  to  sensation  rrhich  could  demand 
their  close  and  direct  union  with  the  Imng  nervous  and  vascular  membrane. 
This  view  derives  great  support  from  the  fact  of  the  existence  of  a stmcture  within 
the  claw  of  the  larger  crustaceans,  which,  so  far  as  the  author  can  learn,  has  not  hitherto 
been  described. 
It  is  generally  stated  that  the  claw  is  entirely  filled  with  the  muscular  apparatus 
belonging  to  it,  but  this  is  by  no  means  the  case.  Neither  the  moveable  piece  or  index, 
nor  the  part  of  the  tarsus  which  it  opposes,  the  pollex,  contain  any  muscular  tissue. 
The  flexor  and  extensor  of  the  index,  terminate  at  the  level  of  the  joint  of  the  pincer, 
where  the  tendon  is  inserted,  and  all  below  this  level  is  filled  with  a spongy  mass 
similar  in  structure  to  that  of  the  internal  integument.  Into  this  mass  the  neiwes  of 
the  limb  principally  pass.  The  muscles  are  supplied  almost  enticely  by  a small  branch, 
while  the  principal  nerve  divides  at  about  the  level  of  the  penultimate  joint  into  two 
trunks,  which  pass  down  one  towards  each  limb  of  the  claw,  and  then  break  up  into 
their  terminal  branches,  which  are  distributed  to  the  spongy  tissue  of  the  claw.  The 
bristles  of  the  claw  in  the  Lobster  are  placed  in  regular  series  of  short  tufts  along  the 
sharp  margin  of  the  index,  protected  by  the  fine  tubercles  which  stud  this  edge,  and 
beyond  which  they  do  not  project.  On  the  broad,  heavily  tuberculated  border  of  the 
larger  claw,  the  bristles  are  often  entirely  absent ; but  the  communication  between  this 
margin  and  the  pulp  within,  is  maintained  by  means  of  a line  of  numerous  canals 
situated  principally  at  the  sides  of  the  tubercles,  never  on  them,  which  reach  to  the  sur- 
face, and  there  terminate  in  bulbous  extremities,  which  contain  the  same  matter  as  that 
found  in  the  cavities  for  the  hairs  (fig.  2 h).  These  bulbous  extremities  of  the  canals, 
which  have  much  the  appearance  of  imperfectly  developed  hairs,  sometimes  project  a 
little  beyond  the  level  of  the  external  surface  of  the  shell,  sometimes  lie  below  and  are 
lodged  in  depressions  in  it. 
In  the  Crab’s  claw,  where  the  tubercles  are  deficient,  and  the  limbs  of  the  pincers 
comparatively  small,  the  tufts  of  bristles  give  place  almost  entii’ely  to  these  hairless 
pulp-cavities.  The  structures  within  are  the  same  as  in  the  Lobster,  but  on  a much  less 
developed  scale. 
Here,  then,  lodged  within  the  densest  part  of  the  shell,  is  a structure  richly  supplied 
with  nerves,  shut  off  from  other  parts  of  the  body,  and  having  commrmication  with 
the  surface  only  through  the  medium  of  canals,  which  are  sometimes  continued  into 
bristles,  and  sometimes  terminate  in  mere  bulbs.  As  a prehensile  organ,  the  claw’ 
probably  needs  sensibility ; but  no  force  which  the  animal  could  exercise  could  make 
any  impression  on  the  parts  within,  through  its  dense  tuberculated  edges.  On  the  other 
hand,  it  is  difficult  to  assign  any  office  to  the  bristles,  and  still  more  to  the  bulbs, 
mechanical  or  otherwise,  except  that  which  has  been  here  suggested, — that,  establish- 
ing, as  they  do,  a communication  between  the  external  smLace  and  the  contained 
nervous  structure,  they  communicate  impressions  to  it,  and  are  in  fact  tactile  organs. 
