806 
ME.  HAI^COCK  OJf  THE  OEHAXEZATIOX  OF  THE  BEACHIOPODA. 
Alimextaey  System. 
It  will  be  convenient  to  commence  the  description  of  the  digestive  apparatus  with 
that  of  the  brachial  appendages,— those  beautiful  and  comphcated  organs  so  charac- 
teristic of  the  BracMo])oda^ — not  from  any  con\action  that  they  are  essentially  portions 
of  this  apparatus,  but  from  their  connexion  with  the  sustentation  of  the  animal,  and 
from  their  position  at  the  commencement  of  the  alimentary  tube,  it  seems  the  natural 
course  to  pursue. 
These  organs  are  variously  modified  in  the  different  families,  and  in  the  Tereh'atv.lidce 
are  supported  upon  a calcareous  loop,  in  connexion  with  the  dorsal  valve,  more  or  less 
developed  in  the  different  species.  In  Waldheimia  this  loop'  originates  in  the  hinge- 
plate  in  two  necks  or  processes, — the  crura,  from  which  two  points  project  downwards, 
called  the  crural  processes.  The  upper  or  dorsal  members  of  the  loop,  passing  from 
these  two  lateral  necks,  stretch  forward  for  about  two-thuxls  the  length  of  the  valve, 
then  bend  towards  the  ventral  valve,  and  turning  back  upon  then’  course,  are  united 
across  the  median  line  a short  way  in  advance  of  the  crural  processes.  The  lateral  por- 
tions of  the  loop  are  curved  a little  outwards.  The  whole  of  this  calcareous  support, 
including  the  crura  and  crural  processes,  is  a product  of  the  inner  lamina  of  the  dorsal 
pallial  lobe.  This  lamina,  with  the  exception  of  a portion  at  each  side,  which  is  con- 
tinuous with  the  similar  lamina  of  the  ventral  lobe,  forming  with  it  the  anterior  wall  of 
the  perivisceral  chamber,  is  turned  downwards  and  forwards,  and  extends  as  far  as  the 
transverse  portion  of  the  loop.  It  then  divides  into  two  lobules,  one  passing  to  the 
anterior  extremity  of  each  of  the  lateral  portions  of  this  calcareous  support,  binding 
together  the  dorsal  and  ventral  members.  The  loop  in  its  sinuous  course  follows  the 
margins  of  this  bifurcated  pallial  process,  and  lies  imbedded  in  its  substance. 
The  arms^  themselves  taper  to  fine  points,  having  taken  their  origin  at  each  side  of 
the  mouth,  which  is  situated  at  the  back  of  the  pallial  chamber  in  a central  position, 
opening  downwards.  They  pass  outwards  and  forwards  in  connexion  -with  the  calcareous 
loop  and  the  pallial  lobules,  running  along  the  outer  edge  of  the  dorsal  member  of  the 
former ; they  then  turn  back  upon  the  refiected  or  ventral  part  of  it,  and  on  reaching  the 
transverse  portion  bend  inwards  and  doubling  sharply  upon  themselves,  again  advance 
and  go  to  form  two  vertical  spirals  turned  towards  the  dorsal  valve.  Tlie  sphals  are 
placed  parallel  to  each  other,  and  throughout  the  coil,  consistmg  of  two  or  three  tiuns, 
they  are  united  across  the  median  line  by  a rather  wide,  stout,  semi-cartilaginous  mem- 
brane, which  is  attached  behind  to  the  transverse  portion  of  the  loop. 
The  arms  are  normally  composed  of  a membranous  tube  or  canal  bearing  a semi- 
cartilaginous  grooved  ridge®.  The  latter  stretches  from  end  to  end  of  the  former,  and 
gives  support  to  the  fringe  of  cirri.  As  far  back  as  the  commencement  of  the  spirals 
the  arms  are  as  above  stated ; but  for  the  entue  length  of  the  lateral  portions  of  the 
loop,  where  the  arms  are  doubled  upon  themselves,  and  where,  of  course,  two  tubes  or 
canals  might  have  been  expected,  there  is  only  one,  the  two  having,  as  it  were,  coalesced. 
^ Plate  LYI.  fig.  3. 
Plate  LII.  figs.  4,  5. 
Plates  LV.  fig.  1 ; LVII.  fig.  2. 
