IME.  HANCOCK  ON  THE  OEGANIZATION  OE  THE  BEACHIOPODA. 
847 
minute  round  ganglion,  from  which  issues  a delicate  filament ; but  these  cannot  be  traced 
far  on  account  of  the  large  blood-lacunes  situated  at  the  root  of  the  gullet ; and  indeed 
neither  these  ganglia  nor  the  filaments,  which  are  all  that  has  been  observed  of  the 
visceral  nervous  system,  have  been  determined  with  sufficient  accuracy.  On  the  upper  or 
anterior  portion  of  the  collar  there  are  two  inconspicuous  ganglia,  which  are  small, 
though  considerably  larger  than  those  just  alluded  to ; they  are  elongated  transversely, 
and  are  placed  considerably  apart,  one  on  each  side  of  the  median  line ; they  give  off  a 
few  minute  filaments,  which  go  to  the  parts  immediately  about  the  mouth,  but  their 
exact  destination  could  not  be  determined,  as  the  tissues  are  very  opake  and  the  fila- 
ments excessively  minute.  These  ganglia  are  apparently  the  homologues  of  the  labial 
ganglia  of  the  Lamellibranchs,  and  probably  of  that  portion  of  the  cerebroids  in  the 
encephalous  Molliisca  which  gives  nerv^es  to  the  lips  and  channel  of  the  mouth.  The 
cord  with  these  two  pairs  of  minute  ganglia,  as  well  as  the  large  subcesophageal  ganglia, 
lie  between  the  two  membranes  composing  the  parietes  of  the  body ; so  it  would  appear 
that  these  important  organs  are  bathed  in  the  blood  flowing  in  the  peripheral  lacunes. 
No  material  variation  has  been  observed  in  the  ganglia  or  nerves  in  any  of  the  articu- 
lated Brachiopods.  In  W.  cranium^ ^ however,  the  subcesophageal  ganglia  are  slightly 
altered  in  form.  The  central  one  is  narrower  than  in  the  other  species,  and  the  lateral 
pair  are  thickest  in  fi’ont  and  taper  backwards. 
In  all,  the  nerves  are  distinctly  striated,  as  if  composed  of  nerve-tubes,  and  each  is 
apparently  provided  with  a neurilemma.  By  far  the  greater  portion  of  the  ganglionic 
mass,  as  already  pointed  out,  is  placed  below  the  alimentary  tube.  This  is  not,  how- 
ever, by  any  means  exceptional  in  the  Molliisca ; and  the  ganglia  do  not  exhibit  that 
distinct  globular  structure  so  common  in  these  animals,  but  seem  to  be  composed  of 
minute  granules.  The  structure,  however,  of  the  central  portions  of  the  system  is  diffi- 
cult to  observe,  on  account  of  the  thickening  of  the  membranes  with  which  they  are  in 
connexion. 
No  organs  of  special  sense  have  been  observed,  and  if  any  such  exist  they  will  pro- 
bably be  in  a very  rudimentary  condition.  Indeed,  sight,  hearing  or  smell  could  be 
of  little  use  to  animals  like  the  Brachiopods,  deprived  of  locomotion,  and  firmly  fixed 
for  the  whole  period  of  their  lives  to  one  spot.  Messrs.  Foebes  and  Hanley,  in  their 
‘ Biitish  Mollusca,’  regard  as  ocelli  and  otilitic  capsules  the  red  spots  at  the  bases  of 
the  setigerous  follicles  in  the  mantle  of  T.  caput-sei'pentis  •,  but  these  are  probably 
nothing  more  than  glandular  matter  in  connexion  with  the  growth  of  the  setse.  I have 
not,  however,  examined  this  animal  alive,  an  advantage  that  these  naturalists  have 
apparently  enjoyed. 
I have  not  succeeded  in  detecting  the  oesophageal  ganglia  in  lAngiila.  Professor 
Owen*  speaks  of  the  subcesophageal  ganglia,  and  they  are  also  mentioned  by  Dr.  C.  Vogt®  ; 
but  from  what  is  stated  in  the  memoir,  it  is  pretty  evident  that  the  latter  physiologist 
did  not  satisfactorily  demonstrate  their  existence.  The  pallial  lobes  are  copiously  sup- 
' Plate  LXII.  figs.  12,  13.  Ibid.  ® Op.  cit. 
IIDCCCLVIII.  5 S 
