152 
MR.  R.  OWEN  ON  THE  ANATOMY  OF  THE  BRACHIOPODA. 
The  alimentary  canal  commences  by  a  small  puckered  transverse  mouthy  -which  is 
situated,  as  before  mentioned,  immediately  behind  the  folded  extremities  of  the  arms, 
and  opens  opposite  the  middle  line  of  the  perforated  valve.  The  oesophagus,  after  having 
passed  through  the  membrane  inclosing  the  viscera,  makes  a  shght  turn  upon  itself,  and 
advances  straight  towards  the  opposite  valve ;  it  then  suddenly  expands  into  a  large 
oval  stomach,  from  the  sides  of  which  the  canals  branching  out  into  the  hepatic  follicles 
are  continued.  The  intestine  returns  in  a  direction  towards  the  perforated  valve,  in- 
cUnes  to  the  right  side,  and  makes  a  slight  bend  forwards  before  perforating  the  cir- 
cumscribing membrane,  in  order  to  terminate  between  the  mantle -lobes  on  that  side. 
The  whole  alimentary  canal  thus  forms  a  loop,  whose  convexity  is  turned  towards  the 
imperforate  or  upper  valve.    This  description  is  taken  from  Ter.  psittacea. 
The  liver  is  a  bulky  gland,  of  a  green  colour  and  minute  follicular  texture ;  it  is 
disposed  in  two  principal  masses,  which  lie  on  each  side  the  alimentary  canal,  and 
between  the  two  lateral  arches  of  the  testaceous  loop  in  those  species  of  Terebratula 
which  possess  that  appendage.  In  none  of  the  specimens  dissected  could  I  perceive 
any  trace  of  a  salivary  gland ;  all  the  glandular  structure  in  connexion  with  the  ali- 
mentary canal  bore  the  green  tint  characteristic  of  the  liver.  In  Ter.  psittacea  the 
ramifications  of  the  hepatic  follicles  resemble  those  of  Gorgonia  jiammea ;  the  ultimate 
sacs,  when  viewed  with  a  high  magnifying  power,  exhibited  plainly  the  net- work  formed 
upon  their  parietes  by  the  minute  hepatic  arteries  and  veins. 
In  two  of  the  larger  specimens  of  Ter.  Sowerhii,  the  ova  were  lodged  external  to 
the  liver,  and  had  also  insinuated  themselves  between  the  layers  of  the  mantle-lobes, 
in  close  proximity  to,  and  partly  surrounding  the  branchial  vessels.  They  are  pro- 
bably discharged  in  this  way  from  the  mantle,  having  previously  been  exposed  to  the 
influence  of  the  branchial  currents.  It  is  their  situation,  when  so  far  advanced,  which 
has  tended  to  prevent  the  discovery  of  the  organization  of  the  mantle  that  adapts  it  to 
the  ofiice  of  respiration ;  but  if  sufficiently  young  specimens  are  obtained^,  the  branchial 
vessels  are  seen  unobscured  by  the  ova.  In  Ter.  psittacea  the  ova  were  very  distinct, 
and  arranged  in  elongated  loops,  but  did  not  extend  so  far  along  the  mantle  as  in 
Ter.  Sowerhii.  They  projected  from  the  external  surface  of  the  mantle.  No  structure 
that  could  be  supposed  to  be  distinct  male  or  fecundating  organs  was  present ;  and 
the  generation  of  Terebratula,  therefore,  as  in  the  ordinary  acephalous  Bivalves,  must 
be  regarded  as  the  simplest  kind  of  hermaphroditism. 
In  dissecting  a  Terebratula  I  have  found  it  most  convenient  to  cut  transversely  through 
the  perforated  valve,  so  as  to  leave  the  orifice  and  the  pedicle  connected  to  the  opposite 
valve,  by  which  means  the  disposition  of  the  muscles  is  satisfactorily  seen,  and  the 
delicate  parts  within  are  less  liable  to  be  disturbed  than  by  attempting  to  separate  the 
entire  valve. 
'  a.  Fig.  12,  «  As  in  Figg.  5  to  9,  . 
