﻿30 
  A 
  MONOGRAPH 
  OF 
  THE 
  VICTORIAN 
  SPONGES. 
  

  

  appearance 
  the 
  original 
  Ascon-tiibes, 
  are 
  lined 
  on 
  the 
  outside 
  of 
  their 
  walls 
  by 
  collared 
  

   cells, 
  so 
  that 
  a 
  section 
  across 
  one 
  of 
  these 
  inhalant 
  canals 
  looks 
  like 
  a 
  section 
  of 
  an 
  

   Ascon-tube 
  turned 
  inside 
  out. 
  The 
  tubular 
  oscula 
  are 
  also 
  lined 
  inside 
  by 
  collared 
  cells. 
  

   It 
  is 
  almost 
  impossible 
  to 
  imagine 
  a 
  more 
  complete 
  loss 
  of 
  individuality 
  on 
  the 
  part 
  

   of 
  the 
  Ascon-persons 
  which 
  make 
  up 
  the 
  colony 
  than 
  is 
  exhibited 
  in 
  this 
  sponge. 
  It 
  

   is 
  diflticult 
  to 
  convey 
  in 
  words 
  a 
  clear 
  idea 
  of 
  the 
  real 
  state 
  of 
  the 
  case, 
  but 
  I 
  hope 
  

   that 
  reference 
  to 
  the 
  figures 
  will 
  enable 
  the 
  reader 
  to 
  follow 
  my 
  description. 
  

   Figure 
  1, 
  Plate 
  V., 
  is 
  a 
  slightly 
  diagrammatic 
  view 
  of 
  a 
  young 
  colony 
  cut 
  in 
  half 
  

   vertically. 
  Figure 
  2, 
  Plate 
  V., 
  is 
  a 
  diagram, 
  simplified 
  as 
  far 
  as 
  possible, 
  and 
  

   intended 
  merely 
  to 
  show 
  how 
  the 
  well-defined 
  Ascon-tubes 
  of 
  tlie 
  lower 
  part 
  of 
  the 
  

   colony 
  become 
  transformed 
  into 
  irregular 
  interspaces 
  in 
  the 
  upper 
  portion, 
  and 
  vice 
  

   versa. 
  The 
  layer 
  of 
  collared 
  cells 
  is, 
  as 
  usual, 
  coloured 
  red. 
  As 
  already 
  stated, 
  this 
  

   diagram 
  is 
  very 
  much 
  simplified 
  ; 
  thus 
  all 
  the 
  tubes 
  are 
  made 
  vertical 
  instead 
  of 
  

   branching 
  and 
  ramifying 
  in 
  every 
  direction, 
  and 
  no 
  inhalant 
  canals 
  are 
  represented 
  

   as 
  entering 
  from 
  the 
  sides 
  of 
  the 
  colony 
  as 
  they 
  mostly 
  do 
  in 
  nature. 
  

  

  As, 
  in 
  the 
  upward 
  growth 
  of 
  the 
  colony, 
  the 
  true 
  Ascon-tubes 
  gradually 
  become 
  

   transformed 
  into 
  irregular 
  interspaces, 
  and 
  the 
  true 
  interspaces 
  become 
  gradually 
  

   converted 
  into 
  definite 
  tubes, 
  a 
  transition 
  stage 
  is 
  reached 
  at 
  a 
  certain 
  point 
  in 
  

   which 
  there 
  are 
  no 
  definite 
  tubes 
  at 
  all, 
  and 
  both 
  Ascon-tubes 
  and 
  interspaces 
  are 
  

   represented 
  by 
  a 
  series 
  of 
  irregular 
  cavities. 
  This 
  condition 
  usually 
  prevails 
  over 
  a 
  

   considerable 
  portion 
  of 
  the 
  centre 
  of 
  the 
  colony 
  (the 
  portion 
  marked 
  x 
  in 
  Fig. 
  2, 
  

   PL 
  v.), 
  so 
  that 
  here 
  we 
  have 
  instead 
  of 
  tubes 
  and 
  interspaces 
  two 
  systems 
  of 
  irregular 
  

   cavities. 
  All 
  the 
  cavities 
  of 
  each 
  system 
  communicate 
  freely 
  with 
  one 
  another, 
  but 
  

   the 
  one 
  system 
  never 
  communicates 
  with 
  the 
  other 
  except 
  through 
  the 
  minute 
  

   inhalant 
  pores 
  (prosopyles) 
  in 
  the 
  tube 
  walls, 
  which 
  latter 
  now 
  form 
  a 
  very 
  complex 
  and 
  

   irregular 
  series 
  of 
  undulating 
  membranes 
  dividing 
  the 
  two 
  systems 
  of 
  cavities. 
  It 
  

   is 
  still 
  possible 
  to 
  determine 
  whether 
  a 
  given 
  cavity 
  in 
  the 
  sponge 
  is 
  gastral 
  cavity 
  

   or 
  interspace 
  by 
  examining 
  carefully 
  its 
  bounding 
  membrane, 
  and 
  observing 
  on 
  which 
  

   side 
  the 
  collared 
  cells 
  lie.* 
  The 
  undulating 
  membrane 
  ( 
  = 
  Ascon-tube 
  walls 
  fused 
  

   together) 
  exhibits 
  the 
  usual 
  characteristics 
  of 
  the 
  Ascon-tube 
  wall 
  except 
  for 
  the 
  

   presence 
  in 
  it 
  of 
  the 
  yellow 
  granules 
  described 
  above 
  (p. 
  18). 
  The 
  mesoderm 
  is, 
  

   however, 
  well 
  developed, 
  so 
  that 
  the 
  wall 
  averages 
  about 
  0-035 
  mm. 
  in 
  thickness. 
  I 
  

   have 
  not 
  succeeded 
  in 
  detecting 
  the 
  prosopyles, 
  apparently 
  they 
  are 
  all 
  closed. 
  

  

  Type 
  D. 
  — 
  This 
  type 
  of 
  canal 
  system 
  is 
  exemplified 
  in 
  Lcucosolenia 
  ventricosa. 
  

   In 
  this 
  species 
  the 
  colony 
  forms 
  large, 
  compact, 
  irregular 
  masses, 
  with 
  

   uneven, 
  undulating 
  outer 
  surface 
  rising 
  into 
  mounds 
  and 
  ridges. 
  In 
  the 
  typical 
  

  

  * 
  As 
  the 
  collared 
  cells 
  very 
  readily 
  become 
  detached 
  and 
  float 
  away 
  in 
  spirit 
  specimens, 
  the 
  task 
  is 
  rendered 
  still 
  

   more 
  difhcult, 
  unless 
  the 
  material 
  is 
  very 
  well 
  preserved. 
  If 
  the 
  collared 
  cells 
  have 
  gone 
  we 
  can 
  still 
  tell 
  on 
  which 
  side 
  

   ihey 
  lay 
  by 
  the 
  position 
  of 
  other 
  structures 
  in 
  the 
  wall, 
  as, 
  for 
  example, 
  the 
  position 
  of 
  the 
  spicules 
  and 
  yellow 
  granules. 
  

   In 
  well-preserved 
  specimens, 
  however, 
  collared 
  cells 
  can 
  easily 
  be 
  found. 
  

  

  