840 
MR.  HAjN'COCK  on  the  ORGANIZATION  OR  THE  BRACHIOPODA. 
Pekivisceeal  Chaaibee. 
The  great  cavity'  placed  close  to  the  hinge  of  the  valves,  in  which  the  viscera  are 
lodged,  is  limited  above  and  below  by  the  dorsal  and  ventral  walls  of  the  body,  and  in 
front  by  the  inflection  of  the  inner  lamina  of  the  pallial  lobes.  There  are  no  openings 
leading  into  this  chamber,  except  those  of  the  o^ddncts,  which  have  been  already  sirffi- 
ciently  described.  The  oesophagus  penetrates  the  anterior  wall ; and  in  the  Terehratulidoe 
there  are  two  anterior  prolongations  of  the  cavity  extending  to  the  extremity  of  the  late- 
ral brachial  loops.  These  prolongations,  the  brachial  pouches,  are  formed,  as  before 
explained,  by  processes  of  the  inner  lamina  of  the  mantle.  In  Rhynchonella  there  are  no 
such  prolongations.  The  great  pallial  or  genital  sinuses  open  freely  into  this  chamber  ; 
they  are  merely  continuations  of  it,  and  lie  between  the  two  laminae  of  the  lobes.  In 
W.  australis‘s  there  are  four  of  these  sinuses  in  each  lobe,  two  on  each  side  of  the  median 
line ; they  extend  from  the  front  of  the  chamber  to  the  anterior  border  of  the  lobe. 
The  external  ones  are  very  wide,  and  give  ofi"  eight  or  nine  branches  from  theii’  outer 
margins,  which  dividing  three  or  four  times  dichotomously,  residt  in  small  twigs,  that 
appear  to  terminate  in  a vessel  running  round  the  edge  of  the  lobe  just  'uithin  the  roots 
of  the  marginal  setae ; they  seem,  however,  sometimes  to  end  in  blind  sacs  before  they 
reach  this  vessel.  The  inner  sinuses  are  comparatively  narrow,  and  on  approaching  the 
anterior  border  of  the  lobe  divide  into  two  short  branches  similar  to  those  already 
described.  The  inner  dorsal  sinuses,  which  never  contain  genital  bands,  are  smaller  than 
the  inner  ventral  ones,  and  taper  gradually  forward. 
The  circumpallial  vessels  of  the  two  lobes  were  not  very  satisfactorily  determined ; they 
appear,  however,  to  communicate  with  the  terminal  twigs  of  the  great  sinuses,  to  unite 
posteriorly  at  the  junction  of  the  lobes,  and  as  two  lateral  trunks  to  open  into  the  perms- 
ceral  cavity,  one  at  each  side  of  the  peduncle  immediately  behind  the  cardinal  process. 
There  is  no  modiflcation  to  note  in  the  perivisceral  chamber  in  any  of  the  Terebratu- 
lidce  that  I have  had  an  opportunity  of  examining.  The  pallial  sinuses,  however,  vary 
in  the  several  species.  Thus  in  W.  cranium^,  though  there  are  still  four’  such  sinuses  in 
each  lobe,  the  trunks  are  proportionately  smaller,  and  more  nearly  of  a size ; the  branches 
are  fewer  and  more  attenuated,  but,  as  in  the  other  species,  di^ided  dichotomously  twice 
or  thrice,  without  any  very  marked  symmetry. 
In  T.  caput-serpentis'S  the  four  trunks  may  still  be  recognized;  but  a considerable 
change,  as  previously  noted,  has  taken  place.  Here  the  trunks  are  fused  so  as  to  form 
in  each  lobe  two  large,  lateral  semi-lunar  sinuses,  in  which  the  genitalia  are  placed. 
The  external  margins  of  these  sinuses  give  ofi"  numerous,  rather  delicate  branches,  which 
dividing  dichotomously  run  to  the  pallial  margin ; the  branches  next  the  middle  line, 
which  correspond  to  the  inner  sinuses,  pass  off  from  their  internal  margins,  and  dinde 
once  or  twice. 
' Plates  LII.  fig.  10 ; LVII.  figs.  1,  2 ; LXI.  figs.  1,  2. 
* Plate  LIII.  figs.  3,  4. 
- Plates  LII.  figs.  1,  2 ; LIX.  fig.  1. 
^ Plate  LIII.  figs.  1,  2. 
