﻿A 
  MONOGRAPH 
  OF 
  THE 
  VICTORIAN 
  SPONGES. 
  25 
  

  

  at 
  its 
  upper 
  extremity. 
  The 
  thin 
  wall 
  of 
  the 
  tube 
  is 
  perforated 
  by 
  numerous 
  circular 
  

   inhalant 
  pores 
  (prosopyles) 
  placed 
  in 
  the 
  intervals 
  between 
  the 
  spicules 
  and 
  leading 
  

   directly 
  from 
  the 
  exterior 
  into 
  the 
  gastral 
  cavity. 
  The 
  diameter 
  of 
  the 
  prosopyles 
  

   in 
  the 
  spirit-preserved 
  specimen 
  is 
  about 
  0*01 
  mm. 
  but 
  they 
  may 
  have 
  been 
  a 
  good 
  deal 
  

   larger 
  in 
  life, 
  (According 
  to 
  Haeckel* 
  the 
  inhalant 
  pores 
  [Tnbi 
  porales] 
  are 
  not 
  

   permanent 
  structures 
  but 
  appear 
  and 
  disappear 
  again 
  in 
  the 
  living 
  sponge 
  with 
  no 
  

   regularity. 
  They 
  appear 
  in 
  any 
  part 
  of 
  the 
  tube 
  wall 
  simply 
  by 
  a 
  process 
  of 
  shrinking 
  

   away 
  of 
  the 
  surrounding 
  soft 
  tissues. 
  The 
  ectoderm 
  appears 
  to 
  be 
  the 
  first 
  part 
  to 
  

   give 
  way 
  and 
  the 
  endoderm 
  the 
  last. 
  Then 
  they 
  disappear 
  again 
  by 
  a 
  reversal 
  of 
  the 
  

   process, 
  the 
  collared 
  cells 
  being 
  the 
  last 
  to 
  close 
  in 
  and 
  resume 
  their 
  original 
  position. 
  

   When 
  they 
  have 
  closed 
  completely 
  no 
  trace 
  is 
  left 
  of 
  their 
  existence. 
  Hence 
  it 
  

   happens 
  that 
  in 
  spirit-preserved 
  specimens 
  the 
  prosopyles 
  are 
  often 
  not 
  visible 
  ; 
  they 
  

   are 
  completely 
  closed. 
  In 
  other 
  cases 
  their 
  position 
  is 
  indicated 
  only 
  by 
  gaps 
  in 
  the 
  

   layer 
  of 
  collared 
  cells, 
  the 
  ectoderm 
  and 
  the 
  mesoderm 
  only 
  having 
  closed 
  in. 
  The 
  

   diameter 
  of 
  the 
  fully 
  open 
  prosopyles 
  is 
  usually, 
  according 
  to 
  Hackel, 
  from 
  0*01-0-02 
  

   mm.) 
  The 
  number 
  of 
  the 
  prosopyles 
  is 
  very 
  great, 
  as 
  will 
  be 
  seen 
  by 
  reference 
  to 
  

   Figure 
  1, 
  Plate 
  IV. 
  

  

  A 
  slight 
  advance 
  in 
  complexity 
  is 
  exhibited 
  by 
  Leiicosolenia 
  stolonifer. 
  Here 
  

   the 
  individual 
  Ascon-persons 
  arise 
  from 
  a 
  creeping, 
  tubular, 
  stolon-like 
  structure 
  

   (the 
  spongorhiza) 
  which 
  spreads 
  over 
  the 
  substratum 
  on 
  which 
  the 
  colony 
  is 
  growing 
  

   in 
  every 
  direction. 
  The 
  spongorhiza 
  may 
  perhaps 
  be 
  regarded 
  as 
  the 
  parent 
  of 
  the 
  

   colony, 
  it 
  grows 
  horizontally 
  itself 
  but 
  its 
  buds 
  (the 
  younger 
  Ascon-persons) 
  grow 
  

   upwards 
  and 
  become 
  much 
  wider 
  in 
  diameter 
  than 
  the 
  parent 
  tube. 
  The 
  parent 
  

   spongorhiza 
  also 
  produces 
  short 
  downward 
  outgrowths 
  which 
  serve 
  to 
  attach 
  the 
  colony 
  

   to 
  the 
  substratum 
  on 
  which 
  it 
  grows 
  (PI. 
  I,, 
  Fig. 
  2). 
  A 
  strong 
  tendency 
  to 
  form 
  a 
  

   spongorhiza 
  is 
  also 
  exhibited 
  in 
  Leiicosolenia 
  litcasi 
  but 
  is 
  not 
  so 
  well 
  marked 
  as 
  

   in 
  L. 
  stoloni/er. 
  The 
  spongorhiza 
  is 
  comparable 
  to 
  the 
  similar 
  structure 
  {hydrorhiza) 
  

   found 
  in 
  many 
  hydroids. 
  

  

  The 
  upright 
  Ascon-persons 
  of 
  Leiicosolenia 
  slolonifer 
  resemble 
  those 
  of 
  L. 
  litcasi 
  

   except 
  in 
  their 
  very 
  much 
  greater 
  size 
  and 
  in 
  the 
  greater 
  thickness 
  of 
  the 
  tube 
  wall. 
  They 
  

   rarely 
  branch 
  or 
  anastomose, 
  and, 
  except 
  when 
  very 
  young, 
  each 
  one 
  is 
  provided 
  with 
  

   a 
  wide 
  terminal 
  osculum 
  ; 
  the 
  youngest 
  individuals 
  end 
  blindly. 
  When 
  fully 
  grown 
  

   they 
  attain 
  a 
  height 
  of 
  about 
  35 
  mm., 
  and 
  a 
  diameter 
  of 
  about 
  o-b 
  mm.; 
  they 
  

   narrow 
  slightly 
  towards 
  the 
  osculum. 
  Owing 
  to 
  the 
  unusual 
  thickness 
  of 
  the 
  Ascon- 
  

   tube 
  wall 
  the 
  inhalant 
  pores 
  are 
  somewhat 
  diiferent 
  from 
  those 
  of 
  L. 
  litcasi. 
  They 
  

   are 
  no 
  longer 
  simply 
  circular 
  apertures 
  perforating 
  a 
  thin 
  membrane. 
  The 
  wall 
  of 
  the 
  

   tube 
  averages 
  about 
  0-14 
  mm. 
  in 
  thickness, 
  and 
  its 
  outer 
  surface 
  is 
  extremely 
  uneven. 
  

   Numerous 
  wide 
  apertures, 
  or 
  depressions, 
  lead 
  into 
  irregular 
  canals 
  in 
  the 
  thickness 
  

  

  * 
  " 
  Die 
  KalkBohwiimme 
  " 
  Vol. 
  I., 
  \). 
  220, 
  ct 
  acq. 
  

  

  