792 
ME.  HAI^COCK  ON  THE  OEGANIZATION  OE  THE  BEACHIOPODA. 
terminates  in  a blind  sac  within  the  visceral  chamber ; that  the  so-called  hearts  give  off 
no  arteries,  and  that  they  possibly  open  externally.  Mr.  Huxley  also  describes,  for  the 
first  time,  a system  of  ramified  peripheral  channels,  and  two  or  three  pyriform  vesicles, 
one  of  which  is  attached  to  the  stomach,  and  is  in  connexion  with  a series  of  “ ridges  " 
and  “ bands.”  Some  of  these  ridges  are  stated  to  pass  from  the  so-called  hearts  to  the 
genitalia ; and  the  whole  apparatus  is  regarded  as  forming  a portion  of  the  chculatory 
organs. 
It  is  chiefly  on  the  points  thus  raised  by  Professor  Huxley  and  myself,  respecting  the 
vascular  and  alimentary  systems,  that  there  is  a difference  of  opinion, — Professor  Owex 
maintaining  the  generally  received  belief  in  the  existence  of  an  anal  aperture  situated 
in  the  pallial  chamber  in  the  Terehratulidce,  as  well  as  in  Lingula;  and  that  the  so- 
called  hearts  are  true  vascular  centres  propelhng  the  blood  through  arteries  to  the 
various  organs. 
Such  being  the  case,  a thorough  investigation  of  the  facts  had  become  necessary.  I 
have  therefore  applied  myself  most  diligently  and  earnestly  to  the  subject,  fully  im- 
pressed with  a sense  of  the  weight  of  authority  opposed  to  the  Hews  I entertain  in 
common  with  Professor  Huxley,  and  with  the  most  anxious  deshe  to  estabhsh  the  truth, 
as  it  is  of  some  importance  that  the  anatomy  and  physiology  of  these,  apparently,  much 
misunderstood  animals  should  be  accurately  determined. 
In  a short  communication  which  I made  to  the  Meeting  of  the  British  Association 
held  at  Cheltenham  last  year*,  the  results  up  to  that  time  were  specified,  as  far  as  they 
related  to  the  matters  in  dispute.  On  the  present  occasion,  however,  I shall  not  confine 
myself  to  these  points ; but  purpose  giving  in  the  following  pages,  as  far  as  possible,  full 
and  complete  details  of  the  entire  anatomy  of  such  of  the  Brachiopods  as  have  come 
under  my  observation.  And  here  it  must  be  stated  that  I should  never  have  been  able 
to  enter  upon  this  subject,  with  any  chance  of  success,  had  I not  had  at  my  command 
an  ample  supply  of  specimens,  and  that  I am  indebted  for  this  great  advantage  to  the 
liberality  of  Dr.  Geay,  Mr.  Woodward,  Mr.  Davidson,  Mr.  Huxley,  Mr.  McAxdeew,- 
Mr.  Alder,  and  Mr.  Leckenby.  My  best  thanks  are  therefore  due  to  these  gentlemen 
for  having  placed  at  my  disposal  specimens  of  the  following  species: — Waldheimia 
australis,  W.  cranium,  Terehratulina  caggut-serjgentis,  BhynclioneUa  psittacea,  Lingula 
anatina  and  L.  affinis'^.  These  are  the  only  forms  that  I have  dissected,  though  I have 
enjoyed  the  opportunity  of  seeing  the  animal,  in  a more  or  less  perfect  state,  of  one  or 
two  other  species,  to  which  allusion  will,  occasionally,  be  made  in  the  following  pages. 
The  shells  of  the  Brachiopods  are  now  so  well  kno’wn  that  it  would  seem  quite  miiie- 
cessary  to  give  here  any  detailed  account  of  them.  But  it  may  perhaps  be  as  well  to 
observe  that  they  are  formed  upon  two  distinct  plans,  one  havmg  the  valves  aifficulated, 
the  other  having  them  unarticulated.  Waldheimia  is  a type  of  the  former.  Lingula  of 
the  latter.  Those  with  articulated  valves  have  the  hinge  generally  fiu-nished  uith  teeth 
and  corresponding  sockets,  which  so  lock  the  valves  together,  that  theh  action  is  very 
' Eeport  of  the  British  Association  for  1856 ; Transactions  of  the  Sections,  p.  Ol.  " Note  1,  p.  850. 
