﻿34 
  A 
  MONOGEAPH 
  OF 
  THE 
  VICTORIAN 
  SPONGES. 
  

  

  jype 
  p 
  — 
  This, 
  the 
  last 
  type 
  of 
  reticulate 
  canal 
  system, 
  is 
  obviously 
  a 
  further 
  

   development 
  of 
  type 
  E, 
  and 
  hence 
  especially 
  interesting. 
  It 
  is 
  best 
  exemplified 
  in 
  

   Lcucosolenia 
  wilsoni. 
  The 
  canal 
  system 
  exactly 
  resembles 
  that 
  of 
  Lencosolenia 
  

   proxima 
  except 
  that 
  the 
  mesodermal 
  ingrowths 
  into 
  the 
  gastral 
  cavities 
  of 
  the 
  

   Ascon-tubes 
  are 
  more 
  strongly 
  developed 
  and 
  the 
  collared 
  cells 
  have 
  spread 
  in 
  over 
  

   them, 
  so 
  that 
  the 
  mesoderm 
  is 
  again 
  covered 
  all 
  over 
  by 
  a 
  layer 
  of 
  endoderm. 
  The 
  

   result 
  of 
  this 
  i^roceeding 
  is 
  to 
  divide 
  the 
  Ascon-tubes 
  into 
  a 
  series 
  of 
  irregular 
  and 
  

   incomplete 
  chambers, 
  by 
  means 
  of 
  what 
  Ha3ckel 
  terms 
  " 
  endogastric 
  septa." 
  

  

  The 
  entire 
  sponge 
  forms 
  a 
  low, 
  irregular, 
  encrusting 
  growth 
  (PI. 
  II., 
  Figs. 
  3, 
  4) 
  

   attaclied 
  to 
  the 
  substratum 
  by 
  short, 
  root-like 
  processes. 
  On 
  the 
  upper 
  surface 
  are 
  the 
  

   minute 
  oscula, 
  each 
  on 
  the 
  summit 
  of 
  a 
  small 
  and 
  almost 
  solid, 
  conical 
  projection, 
  and 
  

   also 
  numerous 
  pseudopores 
  which 
  (on 
  the 
  upper 
  surface 
  of 
  the 
  sponge) 
  are 
  elongated 
  

   and 
  slit-like. 
  Owing 
  to 
  the 
  partial 
  blocking 
  up 
  of 
  the 
  Ascon-tubes 
  by 
  the 
  endogastric 
  

   septa 
  the 
  whole 
  sponge 
  acquires 
  an 
  unusual 
  degree 
  of 
  solidity, 
  which 
  is 
  a 
  very 
  

   characteristic 
  feature 
  of 
  the 
  species. 
  

  

  The 
  pseudopores 
  lead 
  direct 
  into 
  the 
  irregular 
  and 
  perfectly 
  empty 
  interspaces, 
  

   about 
  which 
  there 
  is 
  nothing 
  to 
  attract 
  attention. 
  These 
  lead 
  through 
  the 
  inhalant 
  pores 
  

   (prosopyles), 
  which 
  are 
  easily 
  visible 
  in 
  some 
  parts 
  of 
  my 
  preparations 
  and 
  measure 
  

   about 
  0.02 
  mm. 
  in 
  diameter, 
  into 
  the 
  i\.scon-tubes. 
  The 
  Ascon-tubes, 
  after 
  collecting 
  

   several 
  together, 
  open 
  through 
  the 
  minute 
  oscula 
  at 
  the 
  apices 
  of 
  the 
  conical 
  

   projections 
  (PI. 
  VII., 
  Fig. 
  1). 
  The 
  appearance 
  of 
  the 
  Ascon-tubes 
  in 
  section 
  

   varies 
  a 
  good 
  deal 
  in 
  different 
  parts 
  of 
  the 
  same 
  colony 
  and 
  would 
  seem 
  

   to 
  depend 
  upon 
  their 
  age. 
  In 
  parts 
  of 
  the 
  colony 
  which 
  seem 
  to 
  have 
  been 
  

   newly 
  formed 
  they 
  are 
  comparatively 
  thin-walled, 
  the 
  wall 
  of 
  the 
  tube 
  being 
  

   only 
  about 
  0.04 
  mm. 
  in 
  thickness, 
  while 
  the 
  inhalant 
  pores 
  (prosopyles) 
  are 
  clearly 
  

   visible. 
  The 
  mesodermal 
  ingrowths, 
  also, 
  are 
  not 
  nearly 
  so 
  strongly 
  developed 
  

   as 
  in 
  older 
  tubes, 
  consisting 
  simply 
  of 
  a 
  loose 
  network 
  of 
  stellate 
  cells, 
  over 
  which, 
  

   however, 
  the 
  collared 
  cells 
  have 
  already 
  spi'ead 
  themselves. 
  In 
  the 
  older 
  parts 
  of 
  the 
  

   colony 
  the 
  walls 
  of 
  the 
  Ascon-tubes 
  are 
  thicker, 
  the 
  mesodermal 
  ingrowths 
  

   are 
  more 
  solid 
  and 
  the 
  network 
  of 
  stellate 
  cells 
  of 
  which 
  they 
  are 
  at 
  first 
  composed 
  is 
  

   hardly 
  visible 
  through 
  the 
  dense 
  layer 
  of 
  collared 
  cells 
  which 
  invests 
  it. 
  This 
  

   condition 
  is 
  represented 
  in 
  Figures 
  2 
  and 
  3, 
  Plate 
  VII. 
  In 
  the 
  thick 
  walls 
  of 
  the 
  

   Ascon-tubes 
  small 
  stellate 
  cells 
  can 
  be 
  seen 
  imbedded 
  in 
  the 
  gelatinous 
  ground- 
  

   substance. 
  The 
  prosopyles 
  are 
  not 
  visible 
  in 
  my 
  sections 
  of 
  the 
  older 
  parts 
  of 
  the 
  

   colony, 
  being 
  apparently 
  closed. 
  

  

  No 
  spicules 
  are 
  developed 
  in 
  the 
  mesodermal 
  ingrowths 
  in 
  the 
  gastral 
  cavities 
  

   of 
  the 
  Ascon-tubes, 
  so 
  that 
  if 
  any 
  doubt 
  existed 
  as 
  to 
  the 
  position 
  and 
  extent 
  of 
  the 
  

   originally 
  simple 
  and 
  perfectly 
  hollow 
  Ascon-tubes 
  the 
  arrangement 
  of 
  the 
  skeleton 
  

   would 
  be 
  sufficient 
  at 
  once 
  to 
  determine 
  it. 
  

  

  