﻿22 
  A 
  MONOGRAPH 
  OF 
  THE 
  VICTORIAN 
  SPONGES. 
  

  

  merit. 
  The 
  three 
  prmiary 
  rays 
  are 
  spoken 
  of 
  by 
  Hseckel 
  as 
  the 
  facial 
  rays, 
  and 
  the 
  

   fourth 
  as 
  the 
  apical 
  ray. 
  As 
  in 
  the 
  case 
  of 
  the 
  triradiates 
  the 
  quadriradiate 
  spicules 
  

   may 
  be 
  classified 
  as 
  regular, 
  sagittal 
  and 
  irregular. 
  

  

  In 
  some 
  species 
  triradiate 
  spicules 
  pass 
  almost 
  insensibly 
  into 
  quadriradiates, 
  the 
  

   apical 
  ray 
  appearing 
  first 
  as 
  a 
  tiny 
  wart 
  in 
  the 
  centre 
  of 
  the 
  spicule, 
  and 
  only 
  a 
  very 
  

   few 
  quadriradiates 
  occurring 
  amongst 
  a 
  vast 
  majority 
  of 
  triradiates. 
  Sometimes 
  only 
  

   one 
  or 
  two 
  quadriradiates 
  can 
  be 
  found 
  in 
  a 
  preparation, 
  and 
  it 
  is 
  quite 
  impossible 
  to 
  

   be 
  certain, 
  from 
  the 
  mere 
  fact 
  that 
  no 
  quadriradiates 
  at 
  all 
  can 
  be 
  found, 
  that 
  none 
  

   exist 
  in 
  the 
  sponge. 
  Hence 
  the 
  hopelessness 
  of 
  attempting 
  to 
  classify 
  the 
  Calcarea 
  

   by 
  their 
  spicules 
  alone 
  or 
  even 
  principally. 
  

  

  Oxeote 
  Spicules 
  (Oxea). 
  — 
  I 
  use 
  this 
  term 
  for 
  the 
  spicules 
  named 
  by 
  Hseckel 
  

   '^ 
  Stabnadeln," 
  because 
  they 
  resemble 
  in 
  form 
  the 
  siliceous 
  spicules 
  to 
  which 
  the 
  term 
  

   "oxeote" 
  vvas 
  originally 
  applied 
  by 
  Mr. 
  Ridley 
  and 
  myself 
  in 
  our 
  Report 
  on 
  the 
  

   Monaxonida 
  of 
  the 
  " 
  Challenger 
  " 
  Expedition. 
  The 
  oxeote 
  spicule 
  has 
  only 
  a 
  single 
  

   axis, 
  and 
  thus 
  consists 
  of 
  a 
  simple 
  rod 
  which, 
  in 
  its 
  most 
  typical 
  condition, 
  is 
  spindle- 
  

   shaped 
  and 
  pointed 
  at 
  the 
  two 
  ends, 
  which 
  are 
  precisely 
  similar. 
  This 
  typical 
  

   condition, 
  however, 
  is 
  seldom 
  found. 
  The 
  spicule 
  is 
  nearly 
  always 
  curved, 
  and 
  one 
  

   end 
  is 
  nearly 
  always 
  of 
  different 
  shape 
  to 
  the 
  other. 
  It 
  appears 
  to 
  me, 
  however, 
  

   useless 
  to 
  attempt 
  to 
  give 
  special 
  names 
  to 
  all 
  the 
  varieties 
  of 
  oxeote 
  spicules. 
  

  

  Further 
  details 
  as 
  to 
  the 
  forms 
  assumed 
  by 
  the 
  spicules 
  in 
  different 
  species 
  are 
  

   unnecessary 
  in 
  this 
  place, 
  the 
  nomenclature 
  having 
  been 
  explained 
  I 
  must 
  refer 
  the 
  

   student 
  for 
  further 
  particulars 
  to 
  Hisckel's 
  monograph 
  and 
  to 
  the 
  systematic 
  portion 
  

   and 
  illustrations 
  of 
  the 
  present 
  memoir 
  (Plates 
  IX., 
  X., 
  XL). 
  

  

  With 
  regard 
  to 
  the 
  arrangement 
  of 
  the 
  spicules 
  in 
  the 
  Calcarea 
  Homocoela 
  there 
  

   are 
  one 
  or 
  two 
  points 
  of 
  general 
  interest 
  which 
  offer 
  themselves 
  for 
  consideration. 
  

   In 
  the 
  simplest 
  case 
  the 
  skeleton 
  consists 
  of 
  triradiates 
  only, 
  placed 
  side 
  by 
  side 
  with 
  

   considerable 
  regularity 
  in 
  a 
  single 
  layer 
  in 
  the 
  thickness 
  of 
  the 
  mesoderm. 
  If 
  the 
  

   spicule 
  be 
  sagittal 
  it 
  is 
  so 
  placed 
  that 
  the 
  lateral 
  rays 
  and 
  oral 
  angle 
  are 
  directed 
  

   towards 
  the 
  osculum 
  and 
  the 
  basal 
  ray 
  towards 
  the 
  base 
  of 
  the 
  sponge. 
  If 
  quadri- 
  

   radiates 
  be 
  present 
  they 
  appear 
  nearly 
  always 
  to 
  be 
  so 
  placed 
  that 
  the 
  apical 
  ray 
  

   projects 
  through 
  the 
  endoderm 
  into 
  the 
  gastral 
  cavity, 
  generally 
  curving 
  upwards 
  

   toAvards 
  the 
  osculum, 
  and 
  thus 
  affording 
  a 
  protection 
  against 
  the 
  entrance 
  of 
  

   parasites. 
  If, 
  on 
  the 
  other 
  hand, 
  oxeote 
  spicules 
  be 
  present, 
  they 
  seem 
  always 
  

   to 
  lie 
  nearer 
  to 
  the 
  ectoderm 
  than 
  either 
  the 
  triradiates 
  or 
  quadriradiates, 
  and 
  very 
  

   commonly 
  one 
  end,which 
  is 
  usually 
  slenderer 
  and 
  more 
  sharply 
  pointed 
  than 
  the 
  

   other, 
  projects 
  outwards 
  and 
  upwards 
  through 
  the 
  ectoderm, 
  forming 
  a 
  protection 
  to 
  

   the 
  outside 
  of 
  the 
  sponge. 
  The 
  position 
  and 
  arrangement 
  of 
  these 
  three 
  kinds 
  of 
  

   spicules 
  is 
  well 
  illustrated 
  in 
  Leucosolenia 
  liicasi 
  (PI. 
  lY., 
  Fig. 
  1). 
  

  

  