306 
DE.  J.  S.  BOWEEBAm  OJf  THE  A2s"ATOHT 
a much  less  extent,  is  compressed  laterally,  and  has  the  terminal  point  expanded  into  a 
short  broad  tooth. 
Dentato-palmate  iNEQUi-AJsrcHOEATE  (Plate  XXIV.  fig.  58). — Having  the  distal  spatu- 
late  palm  produced  to  the  extent  of  about  half  the  length  of  the  spiculum,  while  the 
proximal  one  is  developed  in  the  same  form  to  only  about  one-fourth  the  length  of  the 
spiculum,  and  having  the  apices  of  the  hami  produced  beyond  the  extremities  of  the 
palms,  each  in  the  form  of  a short  obtuse  tooth.  From  Spongia  -lobata,  Moxtagu,  in 
the  collection  of  Professor  Grant  : X 1060. 
Dentato-palmate  angulated  anchorate  (Plate  XXV.  figs.  1,  2,  3). — I have  found 
this  form  of  spiculum  only  in  Spongia  plumosa,  Montagu.  Each  of  the  hami  appear  as 
if  forcibly  compressed  towards  the  termination  of  the  shaft,  which  seems  to  have  been 
equally  infiuenced  by  the  compression,  so  that  the  hami  have  become  angulated,  as 
represented  in  the  profile  view  of  one  of  the  spicula  (Plate  XXV.  fig.  3).  The  whole 
of  the  spicula  are  dentato-palmate,  and  the  adult  ones  have  the  terminations  of  the  hami 
strongly  produced,  as  represented  in  Plate  XXV.  fig.  1 ; while  in  the  immatui-e  spicula, 
although  the  palms  are  fully  produced,  the  tooth  appears  in  a rudimentarv  condition,  as 
in  Plate  XXV.  fig.  2. 
Spicula  of  the  Sarcode. 
As  the  tension  spicula  of  the  membranes  are  destined  to  strengthen  and  support  those 
tissues,  so  the  numerous  and  beautiful  tribe  of  stellate  spicula  appear  to  be  devoted  to 
connect  and  give  substance  to  the  gelatinoid  sarcode,  which  so  abundantly  covers  the 
whole  of  the  interior  membranous  structures  of  the  sponges  in  which  they  occm-.  It 
is  difficult  at  first  sight  to  determine  the  difference  in  the  office  of  this  class  of  spicula 
and  those  of  the  internal  retentive  ones ; and  it  is  probable  that  in  some  cases,  when  it 
so  happens  that  the  radii  of  the  stellate  forms  rest  on,  and  become  cemented  to  the 
membranous  structures,  they  may  perform,  to  a certain  extent,  the  same  function,  that 
of  assisting  to  connect  the  membranes  and  sarcodous  structimes  more  firmly  together. 
But  generally  speaking  this  is  not  the  case,  and  especially  with  the  smaller  forms  of 
these  organs ; for  in  comparatively  thick  layers  of  sarcode  we  find  them  in  all  parts,  and 
manifestly  unconnected  with  the  membranes  beneath ; and  in  sponges  which  have  under- 
gone such  an  amount  of  decomposition  as  to  leave  the  membranous  structui’es  entirely 
or  very  nearly  free  from  sarcode,  while  we  see  the  retentive  forms  remaining  firmly 
attached  to  the  membranes,  we  rarely  find  the  stellate  ones,  excepting  when  entangled 
among  the  surrounding  spicula  of  the  skeleton.  We  may  therefore  reasonably  con- 
clude, that  their  normal  function  is  that  of  increasing  the  strength  and  substance  of  the 
sarcodous  structure  of  the  sponge. 
In  the  performance  of  this  office  of  strengthening  and  supporting  the  sarcode,  we  find 
a singular  class -of  spicula,  consisting  of  from  three  to  six  rays,  emanating  from  a common 
centre,  and  always  disposed  at  right  angles  to  each  other.  Between  the  extreme  forms 
of  development  of  these  and  the  simple  stellate  spicula,  there  is  a very  great  amount 
of  structural  difference ; but  on  a more  intimate  acquaintance  with  the  intermediate 
