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DE.  J.  S.  BOWEEBAJ^K  ON  THE  ANATOilT 
spiculated  at  one  end  only.  Some  of  them  were  similar  to  figure  8,  but  were  spiculated 
at  both  ends ; while  in  others,  one  or  more  of  the  rays  have  theh  terminations  bifurcated 
as  in  figure  9,  which  represents  a spiculum  with  the  greatest  number  of  bifurcated  radii 
that  I have  yet  seen.  They  vary  also  considerably  in  size;  the  simpler  of  the  two 
forms,  figure  8,  being  much  larger  than  that  represented  by  figime  9. 
Multiangulated  cylindeical  (Plate  XXVI.  fig.  10). — This  singular  httle  fonn  of 
spiculum  occurs  abundantly  in  the  sarcode  of  Geodia  carinata,  Boweebaxk.  MS.  It  is 
angulated  alternately  in  opposite  directions,  at  regular  distances,  from  two  to  six  or 
seven  times.  It  is  extremely  minute ; a full-sized  five-angled  one  measuring  in  length 
T 3^0 4th  of  an  inch,  and  diameter  of  shaft  leeeeth  of  an  inch.  It  is  difficult  to  decide 
whether  this  should  not  be  considered  as  belonging  to  the  membranes ; but  its  extreme 
minuteness  is  not  in  favour  of  that  supposition,  and  in  carefully  focusing  the  specimens 
of  the  spicula  in  situ^  no  two  appear  to  be  imbedded  in  the  same  plane  above  the  inter- 
stitial membranes,  where  they  are  to  be  observed  best.  I have  therefore  considered 
it  as  belonging  to  the  sarcodous  rather  than  to  the  membranous  structures*. 
Spicula  of  the  Gemmules. 
The  spicula  appropriated  to  the  gemmules  of  sponges  occiu-  in  various  modes  of 
disposition. 
1st.  They  are  imbedded  irregularly  in  an  external  envelope  of  the  gemmule,  or  on 
the  surface  of  the  gemmule  itself,  at  right  angles  to  lines  radiating  fr’om  its  centre. 
2ndly.  They  are  arranged  symmetrically  in  the  crust  of  the  gemmule  parallel  to  lines 
radiating  from  its  centre. 
3rdly.  They  are  disposed  in  fasciculi  in  the  substance  of  the  gemmule,  from  the 
centre  to  the  circumference. 
In  the  first  mode  of  disposition  they  are  sometimes  of  the  same  form  as  those  of  the 
skeleton,  but  considerably  less  both  in  length  and  diameter,  to  adapt  them  to  the  office 
they  have  to  perform.  In  other  cases  they  differ  materially  in  both  size  and  form  fr-om 
those  of  the  surrounding  skeleton ; but  in  every  case  with  which  I am  acquainted,  their 
long  axes  are  parallel  to  the  outer  surface  of  the  case  of  the  gemmule,  or  to  the  surface 
of  the  gemmule  itself. 
In  the  second  mode  of  disposition  they  are  immersed  in  the  comparatively  thick  crust 
of  the  gemmule,  their*  long  axes  being  always  at  right  angles  to  lines  radiatmg  fr*om  its 
centre  to  its  circumference.  Their  forms  become  widely  different  from  those  of  the 
skeleton  spicula,  and  especially  adapted  to  their  peculiar  office ; and  their  terminations 
frequently  expand  into  broad  plates,  as  in  Spongilla  fluviafilis,  Johxstox.  Their  forms 
vary  considerably  in  shape  and  structure  in  different  species.  In  the  gemmules  of  some 
sponges,  one  of  these  modes  of  the  disposition  of  tlieir  spicula  only  can  be  observed. 
* Since  the  above  description  was  written,  I have  found  in  a sponge  from  the  iMauritius  specimens  of 
this  form  of  spiculum,  both  simple  and  strongly  spinous,  with  seven  angulations,  and  very  much  lai’ger  and 
longer  than  tlie  one  figured. 
