﻿A 
  MONOGRAPH 
  OF 
  THE 
  VICTORIAN 
  SPONGES. 
  23 
  

  

  C. 
  — 
  The 
  Canal 
  System 
  of 
  the 
  Calcarea 
  Homoccela 
  as 
  Illustrated 
  by 
  the 
  

  

  Victorian 
  Species. 
  

  

  The 
  portion 
  of 
  our 
  subject 
  with 
  which 
  we 
  have 
  now 
  to 
  deal 
  is 
  perhaps 
  the 
  most 
  

   difficult. 
  We 
  have 
  already 
  described 
  the 
  Olynthus 
  type, 
  and 
  have 
  seen 
  that 
  it 
  

   consists 
  essentially 
  of 
  a 
  narrow, 
  thin-walled 
  tube, 
  open 
  at 
  one 
  end 
  only. 
  Now 
  the 
  

   question 
  before 
  us 
  is 
  — 
  Griven 
  a 
  narrow 
  tube 
  capable 
  of 
  indefinite 
  elongation 
  and 
  

   capable 
  also 
  of 
  branching 
  and 
  anastomosing 
  to 
  an 
  indefinite 
  extent, 
  to 
  determine 
  how 
  

   many 
  different 
  forms 
  the 
  sponge 
  colony 
  resulting 
  therefrom 
  may 
  assume. 
  

  

  It 
  will 
  be 
  seen 
  that 
  under 
  the 
  term 
  "canal 
  system" 
  I 
  include 
  not 
  only 
  the 
  canal 
  

   system 
  of 
  the 
  individual 
  Ascon-person, 
  but 
  also 
  that 
  of 
  the 
  sponge 
  colony 
  as 
  a 
  whole. 
  

   This 
  is 
  necessary, 
  for 
  in 
  some 
  cases, 
  as 
  we 
  shall 
  see 
  {e.g., 
  Leiicosolenia 
  cavata), 
  the 
  

   individuals 
  of 
  which 
  the 
  colony 
  is 
  composed 
  are 
  so 
  intimately 
  united 
  together 
  that 
  we 
  

   can 
  no 
  longer 
  disentangle 
  them, 
  and 
  we 
  cannot 
  treat 
  of 
  the 
  canal 
  system 
  of 
  one 
  

   Ascon-tube 
  without 
  at 
  the 
  same 
  time 
  treating 
  of 
  that 
  of 
  its 
  neighbours 
  ; 
  indeed, 
  the 
  

   individuals 
  no 
  longer 
  have 
  each 
  its 
  own 
  canal 
  system, 
  but 
  the 
  colony 
  has 
  a 
  canal 
  

   system 
  common 
  to 
  them 
  all. 
  The 
  canal 
  system 
  of 
  the 
  colony 
  is 
  of 
  course 
  determined 
  

   by 
  the 
  maimer 
  in 
  which 
  the 
  individual 
  Ascon-tubes 
  are 
  united 
  together, 
  and 
  hence 
  in 
  

   describing 
  the 
  canal 
  system 
  we 
  must 
  at 
  the 
  same 
  time 
  describe 
  the 
  form 
  of 
  the 
  colony, 
  

   and 
  vice 
  vend. 
  In 
  the 
  more 
  complex 
  forms 
  of 
  Calcarea 
  Homocoela 
  it 
  is 
  almost 
  as 
  

   impossible 
  to 
  recognise 
  individuals 
  as 
  it 
  is 
  in 
  the 
  most 
  highly 
  developed 
  sponges 
  

   such 
  as 
  the 
  Keratosa, 
  and 
  the 
  term 
  canal 
  system 
  is 
  equally 
  applicable, 
  with 
  the 
  same 
  

   significance, 
  to 
  both. 
  

  

  The 
  Olynthus 
  is 
  the 
  individual 
  unit 
  of 
  the 
  sponge, 
  and 
  must 
  be 
  regarded 
  as 
  a 
  

   single 
  animal 
  developed 
  directly 
  from 
  a 
  single 
  ovum. 
  It 
  may 
  in 
  fact 
  be 
  compared 
  to 
  

   a 
  Hydra. 
  But 
  the 
  Olynthus 
  has 
  generally, 
  like 
  the 
  Hydra, 
  a 
  strong 
  tendency 
  to 
  form 
  

   buds 
  or 
  branches, 
  but, 
  unlike 
  in 
  Hydra, 
  these 
  branches 
  never 
  separate 
  from 
  the 
  

   parent. 
  They 
  form 
  with 
  the 
  parent 
  permanent 
  colonies, 
  as 
  in 
  such 
  hydroids 
  as 
  

   Obelia. 
  Still 
  we 
  have 
  no 
  difficulty 
  as 
  yet 
  in 
  distinguishing 
  the 
  individuals 
  (Ascon- 
  

   persons) 
  which 
  compose 
  the 
  sponge 
  colony 
  from 
  one 
  another, 
  each 
  is 
  only 
  connected 
  

   with 
  its 
  fellows 
  at 
  the 
  base, 
  and 
  each 
  has 
  its 
  own 
  gastral 
  cavity 
  and 
  its 
  own 
  osculum. 
  

   But 
  now 
  the 
  different 
  members 
  of 
  each 
  colony 
  begin 
  to 
  branch 
  more 
  and 
  more, 
  and 
  

   to 
  fuse 
  with 
  one 
  another 
  wherever 
  the 
  branches 
  come 
  in 
  contact, 
  connnunications 
  

   being 
  estabhshed 
  at 
  these 
  points 
  l)etwecn 
  adjacent 
  gastral 
  cavities. 
  Thus 
  more 
  or 
  less 
  

   complex 
  networks 
  of 
  tubes 
  arc 
  formed, 
  and 
  every 
  chance 
  of 
  distinguishing 
  between 
  tlu> 
  

   individual 
  "persons" 
  which 
  compose 
  the 
  colony 
  is 
  lost. 
  We 
  only 
  know, 
  from 
  

   analogy, 
  that 
  the 
  whole 
  sponge 
  is 
  a 
  colony, 
  and 
  not 
  a 
  single 
  individuah 
  in 
  this 
  

   anastomosis 
  of 
  the 
  different 
  members 
  of 
  the 
  colony 
  to 
  form 
  complex 
  neiworl<s, 
  and 
  

   their 
  consequent 
  loss 
  of 
  individuality, 
  tlie 
  si)onge 
  colony 
  differs 
  widely 
  from 
  the 
  

  

  