ilE.  IIAXCOCK  ON  THE  OEOANIZATION  OE  THE  BEACHEOPODA. 
8?>6 
are  any  afferent  and  efferent  trunks  leading  directly  to  and  from  these  so-called  rudi- 
mentary gills.  In  fact,  in  most  of  the  Brachiopods  the  inner  lamina  of  the  pallial 
sinuses  is  more  or  less  bulged  out ; it  only  happens  that  in  L.  anatina  the  bulging  is  to 
a greater  extent,  and  the  sinuses,  being  parallel,  assume  a plaited  or  laminated  character. 
InZ.  affinis  the  sinuses  are  branched*,  and  consequently  the  gill-like  structure  is  not  by 
any  means  so  distinct,  though  the  walls  of  the  sinuses  are  much  inflated^. 
This  modification  of  the  inner  lamina  of  the  mantle  is  much  of  the  nature  of  those 
various  modes  of  increase  of  surface  obseiwed  in  the  pallial  fringes  and  processes  of 
various  mollusks,  all  of  which,  there  can  be  little  doubt,  assist  in  amating  the  blood. 
The  great  extent  of  brachial  organ  is  also  worthy  of  remark.  In  Z.  jjsittacea,  for  in- 
stance, the  arms,  when  stretched  out,  are  4|  inches  long,  being  upwards  of  fom*  times  the 
length  of  the  shell ; and  they  give  support  to  about  3000  chri.  To  accoimt  for  the  enor- 
mous development  of  these  organs,  it  is  necessary  to  look  to  something  beyond  the  susten- 
tation  of  the  animal ; and  the  conclusion  seems  a natural  one,  that  they  are  destined  for 
the  oxygenation  of  the  blood.  Analogy  would  also  lead  to  the  same  conclusion,  whether 
we  look  to  the  Polyzoa,  to  the  Tunicata,  or  to  the  LamelUbrancMata. 
With  regard  to  the  csecal  prolongations  of  the  mantle,  it  has  ah’eady  been  stated  that 
they  can  scarcely  have  anything  to  do  with  respiration,  as  has  been  supposed.  Such  an 
opinion  rests  upon  the  assumption  that  they  open  into  the  outer  pallial  lacimes.  Xow, 
so  far  as  my  observations  go,  they  have  no  communication  at  all  with  them : on  the 
contrary,  they  seem  to  originate  in  the  external  reticulated  layer  of  the  mantle,  and  do 
not  even  penetrate  it;  the  reticulations  can  be  seen  passing  across  their  bases But 
should  they  actually  perforate  this  layer,  there  is  still  the  homogeneous  layer  separating 
them  from  the  pallial  lacunes.  Such  is  the  result  of  a very  attentive  examination  of 
this  point ; and  yet  it  is  with  some  hesitation  that  it  is  enunciated,  as  Dr.  Carpextee, 
than  whom  no  one  is  more  able  to  determine  this  question,  entertains  the  contrary 
opinion.  He  appears  to  have  examined  the  membranes  whilst  in  connexion  with  the 
shell ; my  observations  were  made  after  the  shell  had  been  reduced  by  acid.  The 
difference  of  our  results  may  perhaps  arise  from  the  different  modes  of  investigation ; at 
all  events,  the  subject  is  worthy  of  further  attention. 
It  must,  however,  be  acknowledged  that  the  corpuscles,  almost  always  found  in  these 
caeca,  strongly  resemble  blood-corpuscles ; they  are  of  the  same  colour  and  form ; but  in 
one  instance  they  had  undergone  a very  marked  change  as  to  the  former  character.  On 
placing  a fine  individual  of  W.  australis  in  acid  as  soon  as  the  periostracum  was  removed, 
the  shell  was  observed  to  be  marked  with  large  patches  of  dark  piu-plish  bromi.  These 
jjatches  continued  to  increase  in  intensity  until  the  shell  was  entirely  reduced,  when  the 
coloration  was  found  to  arise  from  the  contents  of  the  pallial  caeca,  which  were  made 
up  of  the  so-called  blood-corpuscles,  all  of  which  were  of  a rich  purple-broun  colour. 
In  other  parts,  where  no  coloration  existed,  the  contents  of  the  caeca  had  their  usual 
appearance,  being  of  a yellowish  hue. 
* Plate  LXVI.  figs.  1,  2,  3.  * Note  3,  p.  851.  ’ Plate  LIX.  fig.  4. 
