156 
MR.  R.  OWEN  ON  THE  ANATOMY  OF  THE  BRACHIOPODA. 
species  of  animal  motion  of  which  we  find  examples  in  the  erectile  tissues  of  higher 
organizations. 
The  brachial  filaments,  when  viewed  through  the  lens,  presented  an  equal  cylindrical 
figure,  and  an  entire  surface  ;  they  are  less  transparent,  and  of  a  more  muscular  tex- 
ture than  those  of  Ter.  Chilensis ;  they  are  also  thicker  and  shorter,  and  more  incur- 
vated.  Their  bases  are  covered  on  the  inner  side  of  the  arms  by  a  small  fold  of 
membrane  ^ 
The  mouth,  a  small  puckered  orifice^,  is  best  seen  by  dissecting  away  the  transverse 
base  of  the  arms.  The  cesophagus^  passes  obliquely  through  the  tendinous  wall  of  the 
viscera,  in  a  direction  towards  the  upper  or  imperforate  valve ;  having  then  passed 
between  the  anterior  shell-muscles,  it  becomes  shghtly  dilated,  and  surrounded  by  the 
liver,  forming  a  less  capacious  stomach  than  in  Terehratula^ .  The  intestine^  is  con- 
tinued straight  to  the  opposite  end  of  the  visceral  cavity,  and  is  there  again  contracted, 
and  making  a  sudden  bend  upon  itself,  passes  in  a  slight  sigmoid  curve  to  the  middle 
of  the  right  side  of  the  visceral  belt,  which  it  perforates  obhquely,  and  terminates 
between  the  lobes  of  the  mantle  about  half  a  Une  below  the  bend  of  the  arm''.  The 
liver''  is  of  a  beautiful  green  colour ;  it  is  a  congeries  of  elongated  follicles  closely  com- 
pacted together,  which  communicate  by  numerous  orifices  with  the  stomach.  There 
is  no  gland,  analogous  to  a  salivary  gland,  anterior  to  the  liver ;  nor  was  any  gland  but 
the  liver  perceptible  in  Terebratula ;  and  in  this  respect  they  resemble  the  ordinary 
Bivalves,  the  mouth  being,  as  in  them,  destitute  of  any  hard  parts  for  comminuting  or 
seizing  alimentary  substances,  and  therefore  not  requiring  the  superaddition  of  salivary 
glands.  The  coats  of  the  stomach  and  intestines  are  thick  and  pulpy,  and  apparently 
glandular. 
Posterior  to  the  liver  the  whole  of  the  visceral  cavity  not  occupied  by  the  muscles 
and  vessels  is  filled  with  grey  masses  of  ova.  In  these  masses  the  distinct  granules 
could  not  be  seen ;  but  between  the  membranes  circumscribing  the  viscera,  ova  of  a 
browner  colour  could  be  more  distinctly  made  out.  These,  I  suspect,  were  on  their 
passage  to  the  mantle-lobes,  where  probably  in  older  specimens  they  would  be  seen. 
Poli  has  beautifully  figured  the  ova  of  Crania  per  sonata,  following  the  course  of  the 
branchial  vessels  and  obscuring  them.  He  consequently  calls  these  the  ovaries,  and 
observes  that  they  agreeably  ornament  the  mantle^. 
In  Terebratula  all  my  attempts  to  trace  the  nervous  system  were  unsatisfactory ;  but 
in  one  of  the  OrhiculcE,  dissected  expressly  for  that  purpose,  I  succeeded  in  detecting 
two  small  ganglia  on  the  side  of  the  oesophagus  next  the  perforated  valve,  from  which 
two  filaments  accompanying  the  oesophagus  through  the  membranous  wall  immediately 
diverge  and  pass  exterior  to  the  anterior  shell-muscles,  accompanying  corresponding 
'  Fig.  12,  ^  y.  Figg.  9.  11.  ^  ^.  Fig.  11.  *  5.  Figg.  7.  8.  9. 11. 
Figg.  7.  8.  9.  11.        e  M.  Figg.  9.  10.  11.  ?  ^.  Figg.  5.  11. 
"  Testacea  utriusque  Sicilise,  vol.  ii.  pi.  xxx.  fig.  24.  Criopus. 
