ME.  HANCOCK  ON  THE  OEG-ANIZATION  OF  THE  BEACJIIOPODA. 
8J7 
In  JF.  australis  the  genitalia'  are  formed  of  thick  bands,  somewhat  convoluted  and 
branched ; they  are  of  a full  yellow  colour,  and  are  thrust  into  the  trunks  and  main 
branches  of  the  great  pallial  sinuses.  There  are  four  of  these  bands,  two  in  each  lobe ; 
those  in  the  dorsal  lobe  are  single  and  occupy  the  two  outer  or  lateral  sinuses,  extend- 
ing from  behind  the  attachment  of  the  occlusor  muscles  to  within  a short  distance  of 
the  anterior  margin  of  the  mantle  : their  posterior  extremities  reach  to  the  perivisceral 
chamber.  The  ventral  pair  extend  as  far  forward  as  the  dorsal,  and  are  double,  that  is, 
each  forms  a loop,  the  free  extremities  of  which  pass  into  the  outer  and  inner  sinuses  of 
the  same  side;  the  looped  portions  lie  within  the  perivisceral  chamber,  at  the  sides 
below  the  pseudo-hearts  or  oviducts. 
These  genital  bands  are  attached  to  the  inner  lamina  of  the  mantle  throughout  their 
whole  extent,  by  a membrane^,  which,  originating  in  this  lamina,  passes  into  a groove 
extending  along  the  under  surface  of  the  genital  band.  The  genital  or  pallial  artery^ 
runs  along  the  edge  of  this  membrane,  and  has  the  reproductive  organ  developed  around 
it.  This  is  the  ob\ious  disposition  of  the  parts  as  apparent  on  a general  examination ; 
but  on  a closer  inspection  there  can  be  little  doubt  that  these  organs  are  developed,  in 
reality,  between  the  two  membranes,  which,  it  will  afterwards  be  seen,  compose  the 
inner  lamina  of  the  mantle,  and,  bulging  out  the  interior  of  these,  become  suspended, 
as  it  were,  in  the  pallial  sinuses. 
The  organs  themselves  vary  considerably  in  size  and  in  the  extent  of  their  ramifica- 
tions, chiefiy  on  account,  apparently,  of  their  state  of  development,  though  not  entirely  so  : 
as  even  when  the  ova  are  mature  there  is  occasionally  a remarkable  diversity.  In  two 
individuals  that  were  examined,  in  which  the  ova  were  fully  developed,  the  genital  bands 
in  one  were  nearly  twice  as  wide  as  in  the  other.  In  other  specimens,  in  which  these 
organs  were  comparatively  small,  ova  were  distinguishable ; but  in  some  none  could  be 
seen.  Those  m which  ova  are  deficient  are  generally  supposed  to  be  the  male  secreting 
organ.  The  form,  colour,  and  general  appearance  of  these  eggless  bands  do  not  difier 
from  those  charged  with  ova ; and  they  certainly  have  very  much  the  character  of  unde- 
veloped ovaries.  Moreover,  the  genitalia  are  very  perceptibly  composed  of  two  elements, 
the  yellow,  ovigerous  substance,  which  forms  the  chief  mass ; and  a red  material,  which  is 
for  the  most  part  distributed  over  the  surface  of  the  organ.  When  the  organ  is  in  a low 
state  of  development,  this  red  matter  forms  a narrow,  irregular  cord"*,  which  runs  along 
the  sides  of  the  band,  and  is  occasionally  spread  over  the  surface  in  spots  and  blotches. 
When  the  ova  are  matime,  this  substance  can  still  be  traced  as  small  specks  on  the  sur- 
face and  throughout  the  mass.  From  what  will  be  shortly  stated,  with  regard  to  the 
genitalia  in  Lingula,  it  seems  probable  that  this  red  matter  may  prove  to  be  the  testis. 
The  minute  structure  of  these  organs  has  not  been  sufficiently  examined ; it  may  be 
stated,  however,  that  the  ova  appear  to  be  developed  in  cells,  and  that  when  the  yellow 
mass,  which  is  deficient  of  eggs,  is  broken  up  and  placed  under  the  microscope,  it  is  found 
‘ Plates  LII.  figs.  1,  2,  3,  10 ; LYII.  fig.  1.  ==  Plate  LV.  fig.  1. 
' Plate  LYI.  fig.  4.  ' Plate  LIII.  fig.  8. 
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