AND  PHYSIOLOGY  OF  THE  SPONGIAD^. 
305 
at  one  extremity  of  the  shaft,  and  considerably  so  at  the  other ; and  as  the  development 
progresses,  the  curves  of  the  fimbrise  are  extended  in  an  outward  direction,  and  become 
angrdar ; the  extremities  of  the  hami  expand  laterally  and  assume  a foliated  appearance, 
as  seen  in  the  distal  or  larger  end  especially  (Plate  XXV.  fig.  6);  but  the  fimbriae  at  the 
smallest  or  proximal  end  of  the  spiculum,  and  the  foliated  extremity  of  the  adjoining 
hamus,  are  still  separated  from  each  other ; and  this  progressive  development  may  be 
observed  in  all  its  stages,  until  the  connexion  of  the  parts  is  completed,  and  the  fully 
developed  form  represented  in  Plate  XXV.  fig.  7,  is  produced.  The  same  progressive 
development  of  this  form  of  spiculum  may  be  traced  in  those  of  Halichondria  lingua^ 
Boweebaxk,  ms.,  a new  species  of  British  sponge  from  the  Hebrides. 
In  the  performance  of  then*  natural  office  in  the  sponge,  we  find  the  same  laws  of 
attachment  and  projection  obtain  that  I have  described  in  treating  of  the  bihamate 
spicula.  In  the  equi-anchorate  forms,  where  the  terminal  palms  or  teeth  are  equally 
developed,  the  shaft  is  attached  by  the  middle  of  the  external  curve ; but  in  the  inequi- 
anchorate  forms,  where  one  palm  is  developed  to  a very  much  greater  extent  than  the 
other,  we  find  the  smaller  one  is  attached  to  the  membrane,  and  the  larger  is  projected  at 
about  an  angle  of  45  degrees.  Generally  speaking,  the  anchorate  spicula,  like  the 
bihamate  ones,  are  irregularly  dispersed  over  the  surface  of  the  membranes,  but  occasion- 
ally, as  in  Halichondria  lingua,  they  are  developed  in  circles  or  rosette-formed  groups. 
As  may  be  imagined,  from  their  office  and  situation  in  a thin  stratum  of  a gelatinoid 
sarcode,  they  are  at  all  times  small,  and  in  many  cases  so  minute  as  to  require  a micro- 
scopic pow'er  of  at  least  600  linear  to  render  their  structure  distinctly  visible.  They 
occur  in  all  parts  of  the  sarcodous  surface  of  the  interior  of  the  sponge,  and  are  fre- 
quently found  in  greater  profusion  than  usual  on  the  inner  or  sarcodous  surface  of  the 
dermal  membrane ; but  I do  not  recollect  an  instance  of  their  occurrence  on  the  outer 
surface  of  that  organ,  while  on  the  sarcodous  or  interstitial  membranes  they  are  fre- 
quently to  be  observed  in  about  equal  proportions  on  both  sides  of  the  same  mem- 
brane. 
It  will  not  be  necessary  to  describe  or  figure  the  whole  of  these  variable  forms  of 
spicula.  I have  therefore  selected  those  only  that  may  be  considered  more  especially  as 
type  forms. 
Tridentate  equi-anchorate  (Plate  XXIV.  fig.  57). — Having  each  termination  equally 
and  fully  developed,  in  the  form  of  two  lateral  and  slightly  palmate,  and  one  central 
attenuated  tooth.  From  an  undescribed  sponge  in  the  collection  of  Mr.  George  Shad- 
bolt  : X 660. 
Bidentate  inequi-anchorate  (Plate  XXIV.  fig.  55). — Each  termination  divided  into 
two  distinct  teeth,  the  distal  ones  being  largely  and  fully  developed,  while  the  proximal 
ones  are  but  slightly  produced.  From  an  undescribed  sponge  from  the*  coast  of  Sicily : 
X660. 
Palmated  inequi-anchorate  (Plate  XXIV.  fig.  56). — Having  the  distal  termination 
largely  developed  in  the  form  of  a cordate  palm,  while  the  proximal  end  is  produced  to 
2 t 2 
