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DE.  J.  S.  BOWEEBAXK  OX  THE  AXATO^TT 
Cylindeical:  iacipieetly*  seined  (Plate  XXVI.  fig.  16).  This  short  stout  form  of 
spiculum  occurs  abundantly  in  the  envelope  of  Spongilla  gregaria,  Botveebaxk,  MS., 
from  the  River  Amazon.  It  is  usually  without  spines,  but  occasionally  a few  incipient 
ones  are  dispersed  over  the  shaft. 
Cylindeical:  entieely  and  eecuevedly  spinous  (Plate  XX'M;.  fi^.  17). — This  large 
and  beautiful  form  of  spiculum  is  abundant  in  the  envelope  of  the  gemmule  of  Spongilla 
alba,  Caetee.  It  has  a considerable  amount  of  curvature,  and  the  spination  is  remark- 
ably bold  and  striking.  Very  few  of  the  spines  issue  from  the  shaft  at  right  angles  to 
its  axis,  and  these  are  always  near  its  middle ; the  remainder  of  the  spines  are  all  cuiwed 
from  the  apices  of  the  spiculum  towards  the  middle  of  the  shaft.  The  spines  are  con- 
gregated m considerable  numbers  at  each  termination  of  the  spiculum,  and  are  larger 
and  more  curved  there  than  on  any  other  part  of  the  shaft. 
Cylindeical:  entieely  seined;  spines  of  the  middle  cylindeical,  those  of  the 
teeminations  conical  and  eecueved. — These  spicula  might  readily  be  mistaken  by  a 
hasty  observer  for  those  of  Spongilla  alba,  but  a closer  observation  exhibits  essential 
differences  in  their  mode  of  spination.  The  spines  are  distributed  over  the  whole  of  the 
spiculum,  and  are  rather  more  numerous  at  the  terminations  than  towards  the  middle 
of  the  shaft.  At  the  ends  of  the  spiculum  the  spines  are  conical,  acutely  tenninated, 
and  are  recurved  towards  the  middle  of  the  shaft ; but  near  the  middle  of  the  spiculum 
the  spines  are  cylindrical,  stout,  obtusely  terminated,  and  occasionally  expanded  or 
branched.  They  are  very  numerous  in  the  envelope  of  the  gemmule  of  Spongilla  cinerea, 
Caetee,  from  the  water-tanks  of  Bombay.  They  are  so  nearly  of  the  same  fonn  as  those 
represented  in  Plate  XXIV.  fig.  17,  as  to  render  it  unnecessary  to  figure  them. 
2nd.  Spicula  disposed  in  lines  eadiating  Feom  the  centee  to  the  ciecumfeeence  of 
THE  GEMMULE. 
Birotulate  and  Boletiform  Spicula. 
The  whole  of  this  beautiful  group  of  spicula  occur  in  the  thick  coriaceous  proper  coat, 
of  the  gemmules  of  the  Spongilladae.  Sometimes  we  have  but  one  form  thus  located,  as 
in  Spongilla  fluviatilis,  Johnston,  where  we  find  them  very  close  together  in  the  case  of 
the  gemmule,  the  outer  rotula  supporting  the  external  membrane,  and  the  inner  one  per- 
forming the  same  office  for  the  internal  one.  At  other  times  we  find  two  distmct  forms 
in  the  coat  of  the  gemmule,  as  in  Spongilla  recurvata,  Boweebank,  MS.,  from  the  River 
Amazon ; the  inner  one  being  slender  boletiform,  and  the  outer  one  multihamate  bho- 
tulate.  In  every  case  these  spicula  are  so  completely  immersed  in  the  thick  coriaceous 
coat  of  the  gemmule,  that  they  are  perfectly  invisible  under  ordinary  circumstances ; and 
it  is  only  after  the  gemmule  has  been  boiled  m nitric  acid  for  a very  short  period,  that 
it  is  rendered  sufficiently  transparent  to  allow  of  the  spicula  being  seen  in  situ. 
The  progressive  development  of  these  forms  of  spicula  is  very  beautifully  exhibited  in 
the  spicula  from  the  gemmules  of  Spongilla  plumosa,  Caetee.  We  fii'st  observe  them, 
