AMD  PHYSIOLOGY  OF  THE  SPONGIAD^. 
321 
Spicula,  the  position  of  which  are  unknown. 
BlEECUKYO-QUATEEIfATE  : MEDIALLY  SEINED  (Plate  XXVI.  fig.  44). — This  spiculum  is 
figured  and  described  by  my  friend  Prof.  Quekett  in  the  ‘ Catalogue  of  the  Histological 
Series  in  the  Museum  of  the  Koyal  College  of  Surgeons,’  plate  11.  fig.  9 p.  187.  A, 
p.  46,  as  a recurvo-temate  form,  but  a careful  examination  of  three  specimens,  for  which 
I am  indebted  to  him,  has  satisfied  me  that  the  terminations  are  quaternate.  The  two 
ends  of  the  spiculum  difier  considerably  in  structure.  At  one  termination  there  is  httle 
or  no  enlargement  of  the  shaft,  and  the  hooks  are  projected  somewhat  upward  as  well 
as  outward,  and  are  so  cuiwed  that  each  forms  nearly  a semicircle ; while  those  at  the 
opposite  end  each  cuiwes  downward  from  its  base  to  its  apex,  describing  not  more  than 
the  foui’th  part  of  a circle ; and  this  end  of  the  spiculum  has  the  shaft  stronger  and  more 
clavate  than  the  other.  The  spines  on  the  shaft  are  more  or  less  curved  in  accordance 
ufith  the  hooks  of  the  larger  end.  From  these  characters  I am  inclined  to  believe  that 
the  spiculum  is  an  internal  defensive  one,  and  that  the  smaller  end,  the  least  recurved, 
is  the  basal  one.  The  two  perfect  spicula  in  my  possession  were  as  nearly  as  possible  of 
the  same  size,  i^ch  in  length.  It  was  obtained  from  some  spongeous  mat- 
ter taken  from  the  base  of  a large  cup-shaped  sponge  in  the  Museum  at  Edinburgh. 
Tubeeculated  fusifoemi-cylindeical  (Plate  XXVI.  fig.  45). — This  beautiful  spiculum 
is  siliceous.  It  has  been  repeatedly  found  in  the  matter  obtained  by  washing  the  roots  of 
Oculina  rosea  and  other  corals  from  the  South  Sea,  by  my  friends  Messrs.  Matthew  Mae- 
SHALL,  Legg  and  Ingall,  but  the  sponge,  whence  it  is  most  probably  derived,  has  never 
yet  been  determined.  It  is  remarkable  as  being  the  only  well-defined  and  perfect  sili- 
ceous spiculum  that  has  yet  been  obseiwed  to  possess  the  short  stout  tubercles  that  are 
so  characteristic  of  its  structure.  Fragments  of  two  other  spicula,  possessing  similar 
characters,  have  been  observed  by  me,  and  are  represented  by  figures  46  and  47.  In  the 
specimen  represented  by  figure  46,  the  tubercles  are  less  in  number,  but  are  considerably 
more  produced,  and  their  terminations  are  more  abruptly  truncated.  In  the  spiculum 
represented  by  figure  47,  they  are  still  more  widely  distributed,  are  shorter  and  more 
inclined  to  be  conical,  so  that  there  is  little  doubt  that  they  have  belonged  to  three 
distinct  species  of  sponge.  But  in  all  three  of  them  there  is  one  peculiarity,  that  of  the 
manner  of  the  disposition  of  the  tubercles  on  the  shafts  of  the  spicula,  where  we  observe 
them  to  be  disposed  in  more  or  less  regular  longitudinal  lines,  and  that  the  tubercles 
forming  each  line  alternate  udth  those  of  the  line  next  to  them,  so  that  they  assume  the 
appearance  of  a spiral  an-angement.  The  close  alliance  in  the  structure  of  these  spicula 
would  seem  to  indicate  the  existence  of  a peculiar  tribe  of  sponges,  with  which  we  are 
at  present  entirely  unacquainted. 
Ac'eeate  : VEETICTLLATELY  SEINED  (Plate  XXVI.  fig.  48). — I obtained  this  singular  form 
from  a parasitical  eponge  from  YVestern  Australia.  This  curious  sponge,  in  the  formation 
of  its  skeleton,  appears  to  have  appropriated  the  spicula  of  every  other  kind  of  sponge 
that  came  within  its  reach,  and  among  a great  variety  of  forms  I found  several  of  the 
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