860 
ME.  HANCOCK  ON  THE  OEG-ANIZATION  OE  THE  BEACHIOPODA. 
of  the  efferent  brachial  canal  laid  open: — a,  portions  of  the  wall  of  this 
canal ; b,  orifices  leading  into  the  cirri ; c,  <?,  afferent  brachial  arteries ; d,  trans- 
verse channels  of  great  brachial  plexus ; e,  portion  of  the  wall  of  great  brachial 
canal ; f,  minute  plexus  at  the  base  of  brachial  ridge. 
Fig.  4.  Terminal  portions  of  two  cirri  deprived  of  their  epithelium : — «,  longitudinal 
ridge  supporting  afferent  brachial  artery;  b,  external  lamina  or  keel;  c,  c, 
blood-corpuscles. 
Fig.  5.  Diagram  of  longitudinal  section  of  marginal  portion  of  valve  in  connexion  with 
the  mantle: — a,  margin  of  valve;  b,  shell  exhibiting  prismatic  structure; 
c,  c,  pallial  cseca  penetrating  ditto ; d,  great  pallial  sinus ; e,  marginal  vessel ; 
f\  outer  lamina  of  mantle;  g,  external  reticulated  layer  of  ditto,  in  which 
the  pallial  cseca  take  their  origin ; 7i,  homogeneous  layer  of  outer  lamina ; 
inner  lamina  of  mantle ; j,  epithelium ; k,  Jc,  membrane  lining  pallial  sinus ; 
I,  epithelium  of  ditto ; in,  outer  pallial  lacunes ; n,  inner  ditto ; o,  marginal 
fold ; p,  one  of  the  setse ; q,  follicle  of  ditto ; r,  prolongation  of  glandular 
matter  of  follicle ; s,  marginal  muscles ; t,  extreme  pallial  margin. 
Fig.  6.  Portion  of  pallial  margin,  the  inner  lamina  partially  removed:-— «,  exti'eme  mar- 
gin ; b,  marginal  fold ; c,  c,  setse ; d,  follicles  of  ditto ; e,  prolongations  of  the 
glandular  matter  of  the  follicles ; f,  circumpallial  muscular  belt ; g,  g,  marginal 
muscles ; h,  outer  lamina  of  mantle,  exhibiting  through  the  inner  homogeneous 
layer  the  bases  of  the  cseca,  i,  i,  and  the  reticulations  of  the  external  layer. 
Fig.  7.  Diagram  of  transverse  section  of  a portion  of  the  mantle: — a,  outer  lamina; 
b,  external  reticulated  layer  of  ditto ; c,  homogeneous  layer  of  ditto ; d,  bases 
of  pallial  cseca ; e,  inner  lamina  of  mantle ; f,  epithelium  of  ditto ; g,  great 
pallial  sinus ; h,  membranous  lining  of  ditto  ; i,  epithelium  of  ditto ; j,  genital 
organ ; k,  membrane  with  its  epithelium  coating  ditto ; I,  membrane  suspend- 
ing genitalia ; m,  genital  or  pallial  artery ; n,  outer  pallial  lacunes ; o,  inner 
ditto ; p,  lacunes  connecting  the  latter  with  the  genital  artery. 
Fig.  8.  Portion  of  the  extreme  pallial  margin,  exhibiting  pallial  caeca  in  various  stages 
of  growth : — a,  pallial  membrane ; b,  clear  spots,  apparently  corresponding  to 
the  bases  of  the  testaceous  prisms ; c,  c,  enlarged  portions  of  caeca ; d,  slender, 
duct-like  portions  of  ditto ; e,  marginal  fold. 
Fig.  9.  A branch  of  one  of  the  hepatic  lobes: — a,  duct,  exhibiting  minute  internal 
laminae ; b,  terminal  caeca. 
Fig.  10.  A ramuscule  of  the  same  branch  a little  enlarged: — a,  duct;  b,  b,  caeca. 
PLATE  LIX. 
Fig.  1.  External  view  of  lateral  half  of  the  dorsal  pallial  lobe  of  W.  australis,  exhibiting 
the  blood-lacunes : — a,  a,  anterior  and  lateral  margins  of  lobe,  armed  with 
setae ; b,  b,  great  pallial  sinuses  laid  open ; c,  c,  portions  of  the  genitalia ; 
