896 
ME.  C.  DE  MOEG-AJf  ON  THE  STEHCTUEE  AND 
In  some  recent  observations  by  Dr.  Eexst  Hackel*,  attention  has  been  directed  to  the 
tissues  immediately  below  the  shell.  Milxe-Edwaeds  had  already  descidbed  this  tissue 
as  consisting  of  three  layers, — an  outer,  thin  and  firm,  but  non-vascular ; an  inner,  resem- 
bling the  serous  membrane  of  the  higher  animals,  and  investing  especially  the  viscera ; 
and  a middle,  soft,  spongy,  and  very  vascular  layer,  which  he  regards  as  a chorium  or 
dermis.  The  tissue  had  also  been  fully  described  by  C.  Schmidt  and  others.  Dr.  Hacked 
is,  however,  the  first  who  has  published,  so  far  as  the  author  can  ascertain,  an  account 
of  the  connexion  of  the  internal  tissue  with  the  hairs.  He  considers  the  external  layer 
of  the  tissue  which  hes  below  the  shell  as  a chitinogenous  layer,  composed  of  epithelial 
cells,  which  he  calls  chitinogenous  cells ; and  he  regards  the  ofiice  of  this  layer,  as  im- 
phed  by  the  name  which  he  has  given  to  it,  to  be  the  formation  of  the  shell,  which  is, 
according  to  him,  a hardened  secretion  of  the  cells,  laid  down  in  layers  like  a cuticle. 
The  soft  tissue  which  lies  below  the  chitinogenous  layer,  he  describes  as  consisting  of 
more  or  less  firm  homogeneous  connective  tissue,  which  supports  the  vessels  and  nerves. 
Now  it  is  the  chitinogenous  layer  alone  which  he  describes  and  figures  as  entering  the 
large  pore-canals  of  the  shell,  and  continuing  on  to  invest  the  hau’-caHty ; and  he  does 
not  appear  to  recognize  any  connexion  between  the  shell  and  hair-canals,  and  the  soft 
vascular  and  nervous  layer  below  the  cuticle  or  chitinogenous  membrane. 
The  object  of  this  paper  is  to  determine  the  true  connexion  of  the  hair’s  and  bristles, 
and  hence  to  indicate  their  probable  use.  Differences  have  been  noticed  in  the  an’ange- 
ment  and  form  of  the  hahs  in  the  animals  which  have  been  examined,  but  the  general 
mode  of  their  connexion  with  the  shell,  and  with  the  parts  internal  to  it,  is  so  much  the 
same  in  all  as  not  to  require  or  even  to  admit  of  special  description. 
Whether  the  shell  is  to  be  regarded  as  the  homologue  of  the  epidermis  of  the  higher 
animals,  is  not  here  a matter  of  any  consequence.  In  its  perfect  and  hardened  state, 
the  tissue  of  which  it  is  composed  is  too  compact  and  dense  to  justify  the  belief  that  it 
is  vascular  or  sensitive.  But  the  tissue  below  it,  which  is  freely  supplied  with  ner'^es, 
may  fairly  be  regarded  as  the  homologue  of  the  chorium  of  the  higher  animals,  and  like 
it,  as  endowed  with  more  or  less  sensibility ; this  must  apply,  however,  only  to  the  vascu- 
lar, soft,  connective  tissue,  not  to  the  chitinogenous  membrane,  which  is  clearly  epidermic. 
Now  the  following  observations  will,  it  is  believed,  prove  that  while  the  hairs  and  their 
corresponding  shell  canals  are  lined  by  the  outer  chitinogenous  membrane,  then’  most  im- 
portant connexion  is  with  the  sensitive  pulp  which  lies  below  it.  The  best  situations  for 
showing  this  are  some  of  those  parts  in  which  the  shell  is  thin,  as,  for  example,  in  the 
antennae  or  in  the  foot-jaws  of  the  larger  Crustacea  (Plate  LXXI.  fig.  1).  If  a section 
des  trachees,  ou  dea  filets  nerveux  peut-etre,  chez  les  especes  a systeme  vasculaire,  des  eanaux  uoiirriciers. 
Nous  voila  done  bien  loin  des  polls  epidermiques  de  la  plante,  et  bien  pres  des  polls  bulboi'des  des  mamnii- 
feres  et  des  plumes  des  oiseaux,  y compris  les  modifications  de  forme,  de  structime,  d’ organisation  qui  se 
rapportent  a la  difierence  des  sejours,  et  des  fonctions  plus  ou  moins  relatives  a la  protection,  a la  statique, 
peut-etre  meme,  a la  sensation  generate.” 
* fiber  die  Gewebe  des  Elusskrebses.  Mullee’s  Arebiv,  1857,  p.  469. 
