812 
ME.  HANCOCK  ON  THE  OEGANIZATION  OF  THE  BEACHTOPODA. 
groove,  at  the  posterior  junction  of  the  arms,  and  is  a simple,  oval,  transverse  slit,  or 
orifice  devoid  of  any  armature.  In  W.  australis  there  is,  however,  a shght  bulging  out 
of  the  posterior  wall  immediately  within  the  orifice,  which  is  somewhat  like  the  valvular 
appendage  in  Plumatella,  and  may  perhaps  assist  in  swallowing.  The  alimentaiw  tube  ^ 
assumes  the  form  of  a siphon  bent  in  the  vertical  plane,  the  arch  turned  towards  the  dor- 
sal valve ; the  oesophagus  represents  the  short,  the  stomach  and  intestine  the  long  arm. 
The  oesophagus  is  of  no  great  length ; it  is  depressed  as  it  passes  through  the  wall  of 
the  body,  and  is  afterwards  slightly  compressed;  it  ascends  hum  the  oral  aperture, 
having  the  points  of  the  crural  processes  on  each  side  behind,  and,  inclining  backwards, 
passes  between  the  occlusor  muscles ; at  some  little  distance  from  the  dorsal  valve  it 
suddenly  bends  backwards  and  downwards,  and  opens  into  the  anterior  extremity  of  the 
stomach,  which  is  of  an  elongated  form,  somewhat  wider  than  the  oesophagus,  and 
about  as  long.  The  stomach  contracts  gently  behind  towards  the  intestine ; this  latter 
being  at  first  about  as  thick  as  the  commencement  of  the  alimentary  canal.  It  con- 
tinues to  descend  at  the  same  inclination  as  the  stomach,  and  tapering  downwards  passes 
between  the  divaricator  muscles  towards  the  ventral  valve,  immediately  behind  the 
termination  of  the  occlusors,  and  in  front  of  the  accessory  divaricators,  where  it  termi- 
nates in  a rounded  point.  This  point  ^ is  attached  to  the  parietes,  or  lining  membrane 
of  the  perivisceral  chamber,  and  is  imperforate ; consequently  there  is  no  anal  outlet  in 
this  species. 
The  walls  of  the  whole  canal  are  exceedingly  firm ; they  never  collapse,  and  are  pro- 
^dded  with  a fibrous  outer  coat,  and  an  inner  mucous  membrane.  In  the  oesophagus  the 
latter  is  comparatively  delicate,  and  is  raised  into  a few,  not  very  conspicuous,  longitu- 
dinal folds®;  in  the  stomach  the  plications  have  also  a longitudinal  tendency;  but  they 
are  not  numerous,  and  are  somewhat  broken  up  into  irregular  rugse.  The  lining  mem- 
brane is  exceedingly  thick  in  the  intestine,  and  is  produced  into  four’  or  five  very  lai-ge, 
longitudinal  plaits^,  which  project  almost  as  far  as  the  centre  of  the  channel.  The  fibres 
of  the  muscular  coat  of  this  portion  of  the  alimentary  canal  are  transverse.  The  whole 
of  the  mucous  membrane  is  extremely  friable,  and  is  consequently  rarely  observed  entiiu, 
especially  in  the  intestine,  where,  unless  the  specimens  be  in  a good  state  of  preserva- 
tion, it  is  always  broken  up,  and  escapes,  in  fragmentary  masses,  on  opening  the  tube. 
The  specimens  examined  by  Professor  Owen  must,  in  this  way,  have  lost  the  lining  mem- 
brane, or  the  “ muco-epithelial  lining”  could  never  have  been  described  as  “ disposed  in 
very  delicate  transverse  plates®,”  And  indeed  the  illustrative  figiu'e  seems  to  prove  this. 
The  liver®,  of  a greenish  colour,  is  composed  of  a congeries  of  ramified  csecal  tubes ; it 
lies  between  the  dorsal  extremities  of  the  occlusor  muscles,  concealing  the  greater  por- 
tion of  the  oesophagus  and  stomach,  and  is  divided  into  two  lateral  portions,  one  on  each 
1 Plates  LII.  fig.  10 ; LVI.  fig.  1 ; LVII.  figs.  1,  2.  = Plate  LIY.  figs.  S,  9. 
" Plate  LVI.  fig.  6.  " Plate  LIY.  figs.  10,  11. 
Introduction  to  Davidson’s  ‘British  Fossil  Brachiopoda,’  p,  13.  pi.  1.  fig.  4. 
® Plates  LII.  figs.  1,  10;  LYII.  figs.  1,  2, 
