﻿A 
  MONOGRAPH 
  OF 
  THE 
  VICTORIAN 
  SPONGES. 
  67 
  

  

  account 
  of 
  the 
  external 
  form 
  and 
  canal 
  system 
  of 
  this 
  remarkable 
  sponge 
  on 
  pp. 
  35, 
  

   36, 
  I 
  need 
  only 
  refer 
  the 
  reader 
  to 
  that 
  description 
  and 
  to 
  the 
  illustrations 
  (PI. 
  II., 
  

   Figs. 
  5, 
  6; 
  PI. 
  V., 
  Figs. 
  3, 
  4; 
  PL 
  VIII., 
  Figs. 
  5, 
  6) 
  and 
  pass 
  on 
  to 
  describe 
  the 
  

   arrangement 
  of 
  the 
  skeleton 
  and 
  the 
  form 
  of 
  the 
  spicules.* 
  

  

  [b.) 
  Arrangement 
  of 
  the 
  Skeleton. 
  — 
  The 
  slceleton 
  consists 
  of 
  rather 
  slender 
  sagittal 
  

   triradiates 
  and 
  quadriradiates 
  and 
  of 
  the 
  " 
  tripod 
  " 
  spicules 
  (triradiate) 
  . 
  The 
  

   triradiates 
  and 
  quadriradiates 
  are 
  arranged 
  in 
  a 
  single 
  layer, 
  though 
  of 
  course 
  with 
  

   frequently 
  overlapping 
  rays, 
  in 
  the 
  mesoderm 
  of 
  the 
  walls 
  of 
  the 
  tubes, 
  the 
  

   quadriradiates 
  with 
  the 
  apical 
  ray 
  projecting 
  freely 
  into 
  the 
  gastral 
  cavity 
  (PI. 
  V., 
  

   Fig. 
  4). 
  As 
  already 
  stated 
  the 
  spicules 
  are 
  sagittal, 
  and 
  in 
  the 
  central 
  Ascoii-tube 
  

   the 
  basal 
  ray 
  points 
  towards 
  the 
  base 
  of 
  the 
  sponge, 
  while 
  in 
  the 
  radiating 
  tubes 
  the 
  

   basal 
  ray 
  is 
  directed 
  towards 
  the 
  outer, 
  blind 
  end 
  of 
  the 
  tube 
  just 
  as 
  in 
  the 
  articular 
  

   tubar 
  skeleton 
  of 
  the 
  Sycons. 
  The 
  " 
  tripod" 
  spicules 
  form 
  a 
  protective 
  layer 
  on 
  the 
  

   outside 
  of 
  the 
  colony, 
  being 
  placed 
  at 
  the 
  blind 
  ends 
  of 
  the 
  radiating 
  tubes 
  with 
  all 
  

   three 
  rays 
  pointing 
  inwards 
  (Pl.V., 
  Fig. 
  4). 
  

  

  (r.) 
  The 
  spicules 
  (PI. 
  XL, 
  Fig. 
  5). 
  

  

  (1.) 
  Triradiates. 
  — 
  Dermal. 
  These 
  are 
  the 
  " 
  tripod 
  " 
  spicules 
  and 
  the 
  

   extent 
  to 
  which 
  they 
  are 
  developed 
  varies 
  in 
  different 
  specimens. 
  

   When 
  fully 
  developed 
  the 
  rays 
  are 
  very 
  stout 
  and 
  curved 
  towards 
  one 
  

   another 
  in 
  such 
  a 
  manner 
  that 
  if 
  the 
  spicule 
  were 
  placed 
  with 
  the 
  

   apices 
  of 
  the 
  rays 
  resting 
  on 
  a 
  level 
  surface 
  the 
  centre 
  of 
  the 
  spicule 
  

   would 
  lie 
  very 
  much 
  above 
  that 
  surface 
  ; 
  towards 
  their 
  apices 
  the 
  

   rays 
  curve 
  outwards 
  again. 
  Rays 
  stout, 
  conical, 
  gradually 
  but 
  not 
  

   very 
  sharply 
  pointed, 
  measuring 
  about 
  0"12 
  by 
  0.02 
  mm. 
  Deep. 
  

   Sagittal, 
  rays 
  long 
  and 
  slender 
  ; 
  angles 
  about 
  etpial 
  ; 
  rays 
  straight, 
  

   or 
  nearly 
  so, 
  fairly 
  gradually 
  and 
  fairly 
  shar})ly 
  })ointed. 
  Basal 
  ray 
  

   longer 
  than 
  the 
  orals, 
  averaging, 
  say, 
  about 
  O'lO 
  by 
  0*0095 
  mm. 
  when 
  

   the 
  orals 
  measure 
  about 
  O'l 
  by 
  0-0075 
  mm., 
  but 
  the 
  size 
  of 
  these 
  

   spicules 
  is 
  subject 
  to 
  a 
  good 
  deal 
  of 
  variation. 
  

  

  (2.) 
  Quadriradiates. 
  — 
  Like 
  the 
  deep 
  triradiates 
  but 
  with 
  longcM' 
  and 
  

   slenderer 
  facial 
  rays 
  and 
  with 
  the 
  addition 
  of 
  w 
  shorttn- 
  ;i))ic'iil 
  ray 
  

   generally 
  rather 
  strongly 
  and 
  often 
  suddenly 
  curved 
  upwards. 
  In 
  a 
  well 
  

   developed 
  example 
  the 
  basal 
  ray 
  measures 
  about 
  ()*24 
  i)y 
  0'()05 
  nun. 
  

   and 
  the 
  orals 
  about 
  0*21 
  by 
  0*005 
  mm., 
  but 
  here 
  again 
  there 
  is 
  a 
  good 
  

   deal 
  of 
  variation, 
  especially 
  in 
  the 
  development 
  of 
  tlu^ 
  apical 
  ray. 
  

  

  (<y.) 
  Affinities. 
  — 
  I 
  hav(^ 
  a 
  good 
  many 
  sp(>('iin(Mis 
  of 
  this 
  spiM'ic^s, 
  wbich 
  is 
  V(M-y 
  

  

  * 
  I 
  may 
  add 
  that 
  tlio 
  coloin* 
  of 
  tho 
  spongo 
  in 
  spirit 
  is 
  Kvoy. 
  "'' 
  npurlv 
  wliiu-, 
  iin.l 
  lln' 
  Ivxiuri- 
  r.illicr 
  soft 
  mid 
  di'lii'iitc. 
  

   Tlie 
  peculiar 
  structuro 
  ol 
  tho 
  cndodenii 
  is 
  doscribod 
  on 
  p. 
  11. 
  

  

  