AND  PHYSIOLOGY  OF  THE  SPONGIADiE. 
303 
Umbonated  bipocillated  bihamate  (Plate  XXIV.  fig.  53). — Having  a slight  pro- 
longation of  the  shaft  through  the  distal  edge  of  one  or  both  of  the  cups ; in  this  case 
through  the  distal  edge  of  the  lower  one  only. 
Plate  XXIV.  fig.  54.  A view  in  profile  of  a unipocillated  spiculum : the  upper  part 
of  the  figure  represents  a side  view  of  the  cup,  while  the  termination  of  the  lower  por- 
tion is  more  than  usually  elongated ; showing  how  the  umbonation  is  produced  on  the 
distal  edge  of  the  spiculum,  represented  by  fig.  53. 
The  transition  from  the  pocillated  bihamate  to  the  more  fully  developed  and  beautiful 
anchorate  spicula  is  easy  and  natural.  The  terminations  are  more  elaborately  adapted 
to  their  retentive  purposes;  and  the  mechanism  of  the  curved  bow,  with  the  broad 
palmate  terminations  of  the  anchor,  which  cost  man  the  accumulated  experience  and 
wisdom  of  ages  to  bring  to  perfection,  is  wonderfully  foreshadowed  in  these  beautiful 
httle  organs. 
Anchorate  Spicula. 
The  anchorate  spicula,  unlike  the  bihamate  forms,  appear  never  to  occur  reversed  or 
contorted,  but  always  to  present  their  terminations  in  the  same  position  as  those  of  the 
bow  of  an  ordinary  ship’s  anchor.  In  some  sponges  they  are  tolerably  uniform  in  shape 
and  proportions,  while  in  others  they  vary  exceedingly,  not  only  while  in  course  of 
development,  but  even  in  their  adult  condition ; they  glide  so  insensibly  from  one  form 
into  another,  that  it  is  difficult  to  draw  a distinction  between  them ; and  yet,  notwith- 
standing this  latitude  in  shape  and  development,  they  are  very  characteristic  of  species, 
as  there  are  always  a sufficient  number  of  fully  developed  ones  that  exhibit  the  normal 
form. 
In  almost  eveiy  case  of  their  occurrence,  beside  the  large  and  fully  developed  organs, 
we  find  a secondary'  series  accompanying  them,  which  are  very  much  smaller  in  size,  and 
vai-y  exceedingly  both  in  symmetry  and  amount  of  development;  and  there  is  every 
appearance  that  they  are  simply  abortive  developments  of  the  larger  and  more  perfect 
organs,  with  which  they  always  appear  to  agree  in  their  normal  characters. 
There  are  two  primary  divisions  of  these  forms  of  spicula, — equi-anchorate,  when 
both  terminations  are  produced  to  an  equal  extent,  as  in  Plate  XXIV.  fig.  57,  or 
Plate  XXV.  figs.  I and  2,  and  inequi-anchorate,  when  the  distal  termination  is  largely 
and  fully  developed,  while  the  proximal  one  is,  comparatively,  produced  to  a very  limited 
extent,  as  in  Plate  XXIV.  figs.  55  and  56  ; each  of  these  is  subiect,  to  a certain  extent, 
to  similar  degrees  of  further  diversity  of  form,  which  may  be  designated  bidentate,  tri- 
dentate  and  palmate.  These  forms  are  in  truth  but  different  degrees  of  development  of 
the  normal  palmate  form ; but  as  we  find  these  variations  constant  in  different  species 
of  sponges,  it  is  desirable  that  they  should  be  separately  designated,  as  they  afford 
excellent  specific  characters.  Thus  in  Halichondria  granulata.,  Boweebank,  MS.,  a new 
British  sponge,  we  find  large  equi-anchorate  spicula,  in  which  the  lateral  expansions  of 
each  end  of  the  curved  shaft  or  bow  which  forms  the  palmate  terminations  of  the  spicu- 
lum extend  along  the  shaft  towards  the  middle  of  the  bow,  very  little  beyond  the  point 
MDCCCLVIII.  2 T 
