﻿A 
  MONOGRAPH 
  OF 
  THE 
  VICTORIAN 
  SPONGES. 
  33 
  

  

  first 
  indication 
  of 
  the 
  subdivision 
  of 
  the 
  gastral 
  cavities 
  of 
  the 
  Ascon-tubes 
  by 
  

   mesodermal 
  ingrowths, 
  is 
  exempHfied 
  in 
  Leucosolenia 
  proxima. 
  

  

  The 
  external 
  appearance 
  of 
  this 
  sponge 
  is 
  represented 
  in 
  Figm-es 
  1 
  and 
  2, 
  Plate 
  II. 
  

   The 
  colonies 
  are 
  small, 
  only 
  about 
  7 
  or 
  8 
  mm. 
  in 
  diameter, 
  and 
  attached 
  to 
  foreign 
  

   objects, 
  such 
  as 
  the 
  stems 
  of 
  Algse, 
  by 
  means 
  of 
  root-like 
  processes. 
  Over 
  the 
  upper 
  

   surface 
  of 
  the 
  colony 
  are 
  numerous 
  small 
  true 
  oscula, 
  each 
  raised 
  on 
  a 
  conical 
  

   projection. 
  The 
  surface 
  of 
  the 
  colony 
  is 
  pitted 
  by 
  numerous 
  pseudopores. 
  Except 
  

   for 
  the 
  ingrowth 
  of 
  the 
  mesoderm 
  into 
  the 
  gastral 
  cavities 
  of 
  the 
  Ascon-tubes 
  the 
  

   canal 
  system 
  agrees 
  with 
  type 
  B, 
  as 
  will 
  be 
  seen 
  at 
  once 
  by 
  reference 
  to 
  Figure 
  1, 
  

   Plate 
  VIII., 
  representing 
  a 
  vertical 
  section 
  through 
  the 
  colony. 
  The 
  pseudopores 
  on 
  

   the 
  outer 
  surface 
  of 
  the 
  colony 
  are 
  oval 
  and 
  measure 
  about 
  0-27 
  mm. 
  in 
  longer 
  

   diameter 
  (in 
  the 
  specimen 
  selected). 
  They 
  lead 
  into 
  perfectly 
  irregular 
  inter- 
  

   spaces 
  between 
  the 
  Ascon-tubes. 
  The 
  Ascon-tubes 
  have 
  thin 
  walls 
  measuring 
  

   about 
  0-028 
  mm. 
  in 
  thickness. 
  The 
  inhalant 
  pores 
  (proso})yles) 
  which 
  perforate 
  the 
  

   tube-walls 
  are, 
  as 
  usual, 
  small 
  circular 
  apertures, 
  easily 
  visible 
  in 
  my 
  preparations 
  as 
  

   areas 
  devoid 
  of 
  collared 
  cells 
  and 
  about 
  0'014 
  mm. 
  in 
  diameter; 
  they 
  may 
  very 
  likely 
  

   be 
  larger 
  when 
  fully 
  opened. 
  The 
  Ascon-tubes 
  of 
  which 
  the 
  colony 
  is 
  composed 
  

   collect 
  together 
  into 
  several 
  larger 
  tubes, 
  each 
  of 
  which 
  leads 
  up 
  to 
  and 
  opens 
  through 
  

   an 
  osculum. 
  

  

  In 
  many 
  of 
  the 
  Ascon-tubes, 
  and 
  especially 
  in 
  the 
  larger 
  branches 
  which 
  lead 
  up 
  

   to 
  the 
  oscula, 
  there 
  is 
  plainly 
  visible 
  a 
  network 
  (PL 
  VIII., 
  Figs. 
  1, 
  2) 
  of 
  large, 
  

   nucleated, 
  stellate 
  cells, 
  sometimes 
  appearing 
  only 
  near 
  the 
  wall 
  of 
  the 
  tube, 
  leaving 
  the 
  

   central 
  portion 
  of 
  the 
  gastral 
  cavity 
  quite 
  empty, 
  but 
  at 
  others 
  stretching 
  right 
  across 
  

   from 
  wall 
  to 
  wall 
  in 
  the 
  section. 
  These 
  stellate 
  cells 
  resemble 
  ordinary 
  mesodermal 
  

   connective 
  tissue 
  cells 
  except 
  in 
  their 
  large 
  size. 
  The 
  network 
  which 
  they 
  form 
  

   inside 
  the 
  gastral 
  cavity 
  remains 
  connected 
  with 
  the 
  mesoderm 
  in 
  the 
  tube-wall 
  by 
  

   means 
  of 
  certain 
  of 
  the 
  long 
  slender 
  processes 
  of 
  the 
  cells, 
  which 
  penetrate 
  between 
  

   the 
  collared 
  cells 
  of 
  the 
  endoderm. 
  It 
  appears 
  to 
  me 
  highly 
  probable 
  that 
  this 
  

   network 
  of 
  cells 
  has 
  a 
  nutritive 
  function 
  and 
  serves 
  to 
  entangle 
  food 
  particles 
  

   floating 
  in 
  the 
  stream 
  of 
  water 
  which 
  flows 
  through 
  the 
  tubes. 
  There 
  is 
  no 
  trace 
  

   of 
  a 
  similar 
  network 
  in 
  the 
  interspaces 
  between 
  the 
  Ascon-tubes. 
  

  

  It 
  seems 
  very 
  strange 
  that 
  the 
  mesoderm 
  should 
  thus 
  break 
  througli 
  the 
  

   endoderm 
  and 
  come 
  to 
  lie 
  on 
  both 
  sides 
  of 
  it. 
  A 
  somewhat 
  analogous 
  occurrence 
  

   takes 
  place 
  in 
  the 
  case 
  of 
  the 
  ovum 
  of 
  Grantia 
  labyr'uithica, 
  which, 
  as 
  I 
  have 
  

   elsewhere* 
  shown, 
  breaks 
  through 
  the 
  ectoderm 
  and 
  hangs 
  suspended 
  in 
  the 
  inhalant 
  

   canals 
  awaiting 
  fertilisation;! 
  l)ut 
  this 
  is 
  only 
  a 
  temporary 
  condition 
  and 
  more 
  easily 
  

   understood, 
  for 
  the 
  ovum 
  at 
  an 
  early 
  stage 
  is 
  known 
  to 
  possess 
  the 
  power 
  of 
  

   amoe])oid 
  movement. 
  

  

  * 
  " 
  studies 
  on 
  tlie 
  Conipiirative 
  Anfitoniy 
  cif 
  SporiRPS, 
  HI. 
  On 
  the 
  Anntoniy 
  of 
  Orantia 
  liihiirinthirii. 
  Curler, 
  and 
  the 
  

   Bocnlleil 
  family 
  Teiolionidw." 
  Quarterly 
  Journal 
  of 
  Microscopical 
  Science, 
  January, 
  IS',11. 
  

  

  I 
  A 
  careful 
  recxauiinalion 
  of 
  niy 
  preparations 
  of 
  (liaiitid 
  Idlnjiiiitliifd, 
  since 
  this 
  was 
  written, 
  has 
  iiiado 
  mo 
  doubt 
  

   the 
  correctness 
  of 
  this 
  observation, 
  it 
  boiug 
  dilllcult 
  to 
  determine 
  the 
  true 
  nature 
  of 
  the 
  cavities 
  in 
  which 
  the 
  ova 
  are 
  

   suspended 
  . 
  

  

  