ME.  HAjyCOCK  ON  THE  OEGANIZATION  OF  THE  BEACHIOPODA. 
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d,  pallial  or  genital  artery  cut  through ; e,  e,  membrane  along  which  tlie  artery 
runs,  and  which  suspends  the  genitalia ; a similar  membrane,  probably  also 
connected  with  an  artery ; g,  nodules  of  reddish  coloured  matter  attached 
to  ditto,  resembling  that  in  connexion  with  the  genitalia ; A,  A,  h,  nerves  ; 
i,  portion  of  epithelium  covering  inner  surface  of  mantle ; j,  external  homo- 
geneous layer,  which,  together  with  its  epithelium,  forms  the  inner  pallial 
lamina ; k,  Jc,  membrane  lining  the  great  sinus ; I,  portion  of  epithelial  lining 
of  sinus  left  adhering  to  the  inner  wall ; m,  m,  m,  external  lamina  of  lobe ; 
w,  outer  reticulated  layer  of  ditto ; o,  o,  o,  blood-lacunes,  forming  the  outer 
pallial  lacunary  system;  points  of  union  of  the  two  layers  between 
which  the  lacunes  are  situated ; inner  pallial  lacunes  or  blood-channels 
communicating  with  the  genital  arteries,  through  the  suspending  membrane, 
and  with  the  outer  pallial  lacunes ; r,  circumpallial  vessel. 
Fig.  2.  Portion  of  the  great  brachial  canal  laid  open,  exhibiting  the  blood-channels  or 
lacunes  in  its  walls : — «,  semi-cartilaginous  or  grooved  ridge  bearing  the  cirri, 
h,  and  the  brachial  fold,  c ; d,  portion  of  stout  membrane  uniting  the  spirals ; 
e,  supposed  afferent  brachial  channel ; f,  plexus  of  lacunes  communicating 
with  ditto,  and  probably  with  great  brachial  plexus ; g,  minute  plexus  at  the 
point  of  union  between  the  channels,  h,  that  encircle  the  arm  and  those  in 
the  membrane  connecting  the  spirals ; A',  plexus  situated  at  the  other  extremity 
of  the  encircling  channels,  and  communicating  with  those  of  the  grooved 
ridge  or  great  brachial  plexus,  i;  J,  transverse  channels  of  great  brachial 
plexus ; k,  afferent  brachial  arteries  ; I,  I,  ditto  entering  cirri ; m,  orifices  lead- 
ing into  cirri ; 7i,  n,  wall  of  small  or  efferent  brachial  canal  cut  through  and 
laid  back. 
Fig.  .3.  Portion  of  dorsal  wall  of  the  perivisceral  chamber,  the  inner  surface  turned  up, 
and  the  epithelium  removed : — a,  granular  lining  membrane ; A,  external  reti- 
culated layer,  in  which  the  pallial  cseca  originate;  c,  delicate  homogeneous 
layer  in  contact  with  ditto ; d,  d,  bases  of  pallial  caeca ; e,  e,  blood-channels  or 
lacunes  charged  with  blood-corpuscles  and  cellular  tissue ; f,  contents  of 
blood-channels  left  adhering  to  the  homogeneous  layer  on  removing  the  lining 
membrane. 
Fig.  4.  Portion  of  the  external  reticulated  and  homogeneous  layers  much  magnified : — 
a,  outer  reticulated  layer ; A,  homogeneous  ditto ; c,  c,  bases  of  the  pallial  caeca. 
PLATE  LX. 
Fig.  1.  Dorsal  view  of  the  animal  of  Ehg7icho7iella  psittacea: — a,  pallial  lobe;  A,  body; 
<7,  peduncle ; d,  d,  great  pallial  sinuses  giving  branches  of  the  margin ; e,  mar- 
ginal fold  ; y,  circumpallial  vessel ; extreme  pallial  margin ; A,  A,  genitalia ; 
i,  i,  muscular  ties  uniting  the  walls  of  the  genital  sinuses ; J,g\  brachial  apparatus 
