850 
SIE.  HANCOCK  ON  THE  OEOANIZATION  OE  THE  BEACHIOPODA. 
in  Paludicella  there  is  a set  of  muscles^  which  acts  in  the  same  way  as  the  parietals,  or 
those  so  instrumental  in  opening  the  valves  of  the  unarticulated  Brachiopods,  as  exhi- 
bited in  Lingula.  The  set  alluded  to  have  been  likewise  denominated  parietal  muscles, 
and  they  are  in  connexion  with  the  mantle  or  lining  membrane  of  the  cell,  their  extre- 
mities being  attached  to  the  cell-wall.  By  their  contraction  they  diminish  the  space 
within  which  the  polype  lies,  and  thus  the  contained  fluid  forces  it  upwards,  and  at  the 
same  time  umnlls  the  tubular  oriflce ; just  as  the  fluid  in  the  perivisceral  chamber  is 
made  to  open  the  valves  by  the  contraction  of  the  anterior  and  posterior  parietes. 
From  their  position  and  function  there  can  be  little  doubt  that  these  muscles  m Lingula 
and  Paludicella  are  homologous.  It  is  also  worthy  of  remark,  that  the  punctures  in  the 
cell  walls  of  Lepralia  resemble  the  perforations  in  the  shell  of  the  Brachiopoda,  as  has 
been  pointed  out  by  Dr.  Caepentee^. 
The  Brachiopods  are  also  very  closely  connected  with  the  Ascidice,  though  the  former 
are  more  highly  organized,  as  evinced  by  the  greater  completeness  of  the  nervous  system. 
In  both,  the  principal  ganglionic  masses  are  below  the  alimentaiy"  canal.  The  relations 
are  however  best  displayed  by  the  circulatory  system,  which  is  developed  on  the  same 
plan  in  both  forms ; the  only  diflerence  being  that  the  large  blood-lacunes  of  the  Asci- 
dian  are  reduced  in  size,  and  are  formed  for  the  most  part  into  minute,  narrow  channels 
by  the  development  of  the  atrial  membrane,  and  by  its  collapse  upon  the  'siscera,  and 
its  extension  and  reflexion  upon  the  walls  of  the  body.  In  these  respects,  however,  the 
genus  Pliallusia  will  bear  comparison  with  the  Brachiopods.  In  both,  too,  there  is  the 
same  unilocular  heart,  imperfect  arterial  system,  and  almost  complete  deflciency  of  veins. 
The  breathing  organ  in  the  Ascidian  has  undergone  a considerable  change ; but  whether 
it  is  or  is  not  morphologically  the  same  as  the  arms  of  the  BracMojpoda,  these  organs  in 
both  forms  are  similarly  related  to  the  mouth. 
The  affinity  of  the  Brachiopod  to  the  Ascidian  is  also  seen  in  the  intimate  connexion 
that  exists  between  the  mantle  and  the  shell ; and  the  csecal  processes  of  the  former, 
which  penetrate  the  shell,  are  probably  the  homologues  of  the  vascular  prolongations 
which  nourish  the  test  of  the  latter. 
The  inferiority  of  the  Brachiopods  to  the  Lamellibranchs  is  evinced  alike  by  the 
digestive,  the  circulatory  and  respiratory  organs,  and  by  the  nervous  system,  notuith- 
etanding  that  the  muscular  apparatus  might  be  assumed  to  be  developed  upon  a higher 
type. 
Notes  added  Felruary  1859. 
No.  I. — I have  been  under  the  necessity  of  naming  this  species,  for  it  does  not  agree, 
as  far  as  can  be  ascertained,  with  any  described  form.  It  was  received  along  uith  two  or 
three  specimens  of  L.  anatina.,  and  it  was  only  after  the  shell  had  been  removed,  and  the 
* Hancock,  “ On  the  Anatomy  of  the  Freshwater  Bryozoa,”  &c.,  Ann.  and  Mag.  Nat.  Hist.  a'oI.  t.  p.  1/3 
(1850). 
- Proceedings  of  the  Eoyal  Society,  vol.  vii.  p.  36  (ISSl). 
