﻿28 
  A 
  MONOGRAPH 
  OF 
  THE 
  VICTOKIAN 
  SPONGES. 
  

  

  Type 
  A. 
  — 
  Leucosolenia 
  dubia 
  consists 
  of 
  a 
  network 
  of 
  tubes 
  spreading 
  in 
  

   many 
  planes 
  and 
  varying 
  in 
  the 
  closeness 
  of 
  its 
  meshes 
  not 
  only 
  in 
  different 
  specimens 
  

   but 
  even 
  in 
  different 
  parts 
  of 
  the 
  same 
  colony. 
  Figure 
  3, 
  Plate 
  I., 
  represents 
  a 
  small 
  

   portion 
  of 
  a 
  colony 
  enlarged 
  four 
  times. 
  We 
  cannot 
  of 
  course 
  distinguish 
  the 
  

   Ascon-persons 
  of 
  which 
  the 
  colony 
  is 
  composed, 
  we 
  can 
  only 
  distinguish 
  between 
  

   what 
  I 
  propose 
  to 
  call 
  Ascon-tnbes 
  and 
  interspaces. 
  The 
  Ascon-tubes 
  are 
  of 
  course 
  

   lined 
  by 
  collared 
  cells 
  (endoderm) 
  and 
  the 
  interspaces 
  by 
  ectoderm. 
  Although 
  the 
  

   interspaces 
  in 
  the 
  outer 
  portions 
  of 
  the 
  colony 
  (and 
  indeed 
  also 
  in 
  the 
  inner 
  portions) 
  

   are 
  often 
  no 
  wider 
  than 
  the 
  Ascon-tubes 
  themselves 
  yet 
  no 
  definite 
  external 
  skin 
  

   (pseiidodenn) 
  is 
  formed, 
  and 
  hence 
  no 
  definite 
  pseudopores. 
  The 
  structure 
  of 
  the 
  

   Ascon-tube 
  is 
  the 
  same 
  as 
  in 
  the 
  Homocoela 
  Simplicia. 
  It 
  is 
  cylindrical 
  and 
  about 
  

   0"5 
  to 
  1 
  mm. 
  in 
  diameter, 
  but 
  varies 
  a 
  good 
  deal 
  in 
  different 
  parts 
  of 
  the 
  same 
  colony. 
  

   True 
  oscula 
  are 
  occasionally 
  visible 
  on 
  the 
  upper 
  surface 
  of 
  the 
  colony. 
  Two 
  or 
  three 
  

   Ascon-tubes 
  open 
  by 
  the 
  same 
  osculum 
  and 
  the 
  diameter 
  of 
  the 
  latter 
  is 
  rather 
  less 
  

   than 
  that 
  of 
  an 
  Ascon-tube. 
  The 
  prosopyles 
  are 
  not 
  visible 
  in 
  my 
  specimens, 
  they 
  

   are 
  probably 
  closed. 
  As 
  the 
  thickness 
  of 
  the 
  tube-wall 
  is 
  unusually 
  great 
  (about 
  

   0-1 
  mm.) 
  the 
  inhalant 
  pores 
  must 
  be 
  elongated, 
  probably 
  they 
  resemble 
  those 
  of 
  

   Leucosolenia 
  stolonifer 
  described 
  above. 
  

  

  Type 
  B. 
  — 
  The 
  simplest 
  example 
  of 
  this 
  type 
  is 
  afforded 
  by 
  Leucosolenia 
  stipitata. 
  

   The 
  entire 
  colony 
  is 
  only 
  about 
  8 
  mm. 
  in 
  height 
  and 
  is 
  perched 
  on 
  the 
  

   summit 
  of 
  a 
  short 
  stalk. 
  Figures 
  4, 
  5, 
  6, 
  Plate 
  L, 
  show 
  the 
  external 
  form. 
  The 
  

   colony 
  consists 
  of 
  a 
  network 
  of 
  Ascon-tubes 
  so 
  disposed 
  that 
  there 
  is 
  one 
  main 
  

   tube 
  running 
  vertically 
  through 
  the 
  centre 
  of 
  the 
  colony, 
  into 
  which 
  the 
  remaining 
  

   tubes 
  debouch. 
  The 
  main 
  tube 
  is 
  probably 
  not 
  to 
  be 
  regarded 
  as 
  the 
  parent 
  stock 
  

   from 
  which 
  the 
  others 
  have 
  been 
  budded 
  out 
  but 
  as 
  formed 
  by 
  the 
  fusion 
  of 
  a 
  number 
  

   of 
  tubes 
  to 
  form 
  a 
  single 
  axial 
  cavity. 
  It 
  is 
  lined 
  throughout 
  by 
  collared 
  cells 
  and 
  

   ends 
  at 
  the 
  summit 
  of 
  the 
  colony 
  in 
  a 
  single, 
  wide, 
  true 
  osculum. 
  Figure 
  2, 
  Plate 
  IV., 
  

   shows 
  a 
  vertical 
  section 
  through 
  the 
  colony, 
  in 
  which 
  the 
  relations 
  of 
  the 
  different 
  

   Ascon-tubes 
  is 
  made 
  clear. 
  From 
  this 
  it 
  will 
  be 
  seen 
  that 
  the 
  interspaces 
  are 
  necessarily 
  

   confined 
  to 
  the 
  peripheral 
  portions 
  of 
  the 
  colony. 
  The 
  outer 
  tubes 
  of 
  the 
  colony 
  are 
  

   very 
  wide 
  and 
  the 
  interspaces 
  between 
  them 
  correspondingly 
  small, 
  hence 
  there 
  is 
  a 
  

   common 
  pseudoderm 
  formed 
  by 
  the 
  outer 
  waUs 
  of 
  the 
  outer 
  tubes, 
  in 
  which 
  the 
  

   interspaces 
  appear 
  as 
  definite 
  pseudopores 
  (PI. 
  I., 
  Fig. 
  6). 
  The 
  pseudoderm 
  is 
  

   strengthened 
  by 
  spicules 
  of 
  somewhat 
  greater 
  size 
  than 
  those 
  found 
  in 
  the 
  interior 
  of 
  

   the 
  colony. 
  The 
  walls 
  of 
  the 
  Ascon-tubes 
  are 
  very 
  thin 
  and 
  the 
  prosopyles 
  are 
  very 
  

   clearly 
  visible 
  in 
  my 
  stained 
  preparations 
  both 
  in 
  the 
  inner 
  and 
  outer 
  tubes 
  of 
  the 
  

   colony 
  ; 
  they 
  are 
  circular 
  apertures 
  about 
  0*02 
  mm. 
  in 
  diameter. 
  

  

  Another 
  good 
  illustration 
  of 
  this 
  type 
  is 
  found 
  in 
  Leucosolenia 
  pulcherrima, 
  

   the 
  only 
  point 
  of 
  difference 
  to 
  notice 
  as 
  regards 
  the 
  canal 
  system 
  being 
  the 
  presence 
  

  

  