794 
ME.  HANCOCK  ON  THE  OEGANIZATION  OE  THE  BEACHIOPODA. 
are  partially  buried  in  the  parietal  membrane,  and  are  generally  seen  shining  through 
of  a yellow  colour. 
No  anal  aperture  can  be  detected  in  any  of  the  articulated  Brachiopods  that  have 
come  under  my  observation,  either  at  the  point  where  the  intestinal  tube  terminates  or 
within  the  pallial  cavity,  or  anywhere  else.  Thus  it  would  appear  that  in  this  group 
there  are  three  external  orifices,  two  being  at  the  apices  of  the  pseudo-hearts,  the  third 
is  the  mouth.  In  Rhynchonella^ , however,  there  are  five  openings,  this  genus  having 
four  of  the  so-called  hearts  or  oviducts,  two  of  which  are  situated  as  in  the  Terehratulidce. 
and  two  above  the  mouth,  one  being  at  each  side  of  the  liver. 
In  Lingula'^  the  body  of  the  animal  is  depressed,  and  occupies  a much  larger  portion  of 
the  shell-cavity  than  it  does  in  either  the  Terebratulidoe  or  BhyncJionellidce.  The  pallial 
lobes  are  rather  stout;  but  the  great  sinuses  are  nevertheless  distinctly  seen  through 
their  membranes ; they  are  not  united  behind,  as  in  the  articulated  Brachiopods,  but  are 
free  and  extend  some  distance  from  the  body  all  round  the  posterior  or  umbonal  region. 
The  body  thus  becomes  well  defined,  the  lateral  walls  being  at  right  angles  to  the 
dorsal  and  ventral.  The  two  latter  are  very  delicate,  and  so  transparent  that  the  viscera 
are  quite  apparent  through  them,  the  liver  and  genitalia  being  the  most  conspicuous. 
The  lateral  parietes  are  strong  and  muscular,  and,  having  theii'  edges  attached  to  the 
valves,  give  a definite  form  to  the  enclosed  space,  which  is  wide,  rounded  in  front  and 
tapering  backwards. 
On  turning  back  the  ventral  pallial  lobe®  the  arms  are  observed  occupying  the  greater 
portion  of  the  pallial  chamber,  which  is  about  half  the  length  of  the  shell.  The  mouth 
is  situated,  as  in  the  Terebratulidce,  in  the  brachial  groove ; and  on  each  side  of  it,  a 
little  below,  are  the  ovarian  outlets,  which  penetrate  the  anterior  wall  of  the  body.  On 
the  right  side  of  the  animal,  between  the  margins  of  the  mantle,  is  placed  the  anal 
orifice,  which  is  very  distinct  and  easily  detected. 
The  best  view  of  the  viscera  is  obtained,  in  the  articulated  forms,  by  lading  open  the 
dorsal  wall  of  the  body,  along  the  central  line,  from  the  umbo  to  the  anterior  wall.  In 
this  way  all  the  organs'*  are  seen  in  their  natural  positions,  hung  within  the  peririsceral 
chamber.  The  alimentary  tube  is  observed  extending  from  the  front  to  the  posterior 
extremity  of  the  chamber,  the  anterior  portion,  the  stomach,  being  somew  hat  enlarged, 
and  partially  concealed  beneath  the  two  lateral  dirisions  of  the  folliculated  liver.  The 
true  heart,  in  the  form  of  a rather  large,  pyriform  vesicle,  is  appended  to  the  dorsal  sur- 
face of  the  stomach ; and  on  each  side  of  the  chamber,  above  and  below%  is  an  accessory 
pulsatile  vesicle.  A little  behind  the  heart,  at  the  sides,  are  the  oriducts,  two  large 
funnel-shaped  organs  with  laminated  interiors, — the  hearts  of  Professor  Oavex.  The 
four  genital  organs  are  placed  at  the  sides,  above  and  below%  protruding,  from  the  great 
pallial  sinuses,  into  the  perivisceral  chamber ; and  the  various  muscles  are  seen  arranged 
at  each  side  of  the  alimentary  tube  stretching  from  wall  to  Avail. 
* Plates  LV.  fig.  3 ; LX.  fig.  3.  ^ Plates  LXIV.  figs.  1,  2 ; JjXYI.  figs.  1,  3. 
’ Plates  LXIV.  fig.  3 ; LXVI.  fig.  2.  ^ Plates  LII.  fig.  10 ; LIII.  fig.  5 ; LIT.  figs.  1,  2. 
