﻿44 
  A 
  MONOGRAPH 
  OF 
  THE 
  VICTORIAN 
  SPONGES. 
  

  

  Subsection 
  1. 
  Indivisa. 
  

  

  The 
  gastral 
  cavities 
  of 
  the 
  Ascon-tnbes 
  composing 
  the 
  colony 
  retain 
  their 
  

   primitive 
  hollow 
  condition, 
  there 
  being 
  no 
  ingrowths 
  of 
  mesoderm 
  or 
  endoderm. 
  

  

  Subsection 
  2. 
  Snbdivisa. 
  

  

  The 
  gastral 
  cavities 
  of 
  the 
  Ascon-tubes 
  are 
  more 
  or 
  less 
  completely 
  subdivided 
  

   into 
  chambers 
  by 
  ingrowths 
  of 
  mesoderm 
  or 
  of 
  both 
  mesoderm 
  and 
  endoderm. 
  

  

  Section 
  3. 
  Homoccela 
  Radiata. 
  

  

  Homocoela 
  in 
  which 
  the 
  sponge 
  consists 
  of 
  a 
  single, 
  central 
  Ascon-tnbe 
  from 
  

   which 
  secondary 
  tubes 
  are 
  budded 
  off 
  radially. 
  

  

  This 
  classification 
  will, 
  so 
  far 
  as 
  I 
  am 
  awai'e, 
  serve 
  to 
  include 
  all 
  the 
  known 
  forms 
  

   of 
  Homocoela 
  with 
  the 
  doubtful 
  exceptions 
  of 
  Ha^ckel's 
  Ascoinctra 
  and 
  von 
  Lendenfeld's 
  

   Lencopsis,^ 
  concerning 
  both 
  of 
  which 
  we 
  require 
  further 
  details. 
  Ascoinetra 
  may, 
  as 
  I 
  

   have 
  already 
  suggested, 
  simply 
  represent 
  a 
  series 
  of 
  ontogenetic 
  stages 
  present 
  at 
  the 
  

   same 
  time, 
  for 
  there 
  can 
  be 
  little 
  doubt 
  that 
  the 
  most 
  complex 
  adult 
  forms 
  pass 
  

   through 
  several 
  stages, 
  beginning 
  with 
  the 
  Olynthus, 
  in 
  their 
  life 
  history 
  ; 
  while 
  the 
  

   extremely 
  doubtful 
  Lencopsis 
  is 
  probably 
  only 
  one 
  of 
  the 
  Homoccela 
  reticulata, 
  and 
  

   whatever 
  it 
  is 
  it 
  is 
  so 
  insufficiently 
  described 
  that 
  we 
  cannot 
  possibly 
  recognise 
  it. 
  

  

  In 
  distinguishing 
  species 
  all 
  characters 
  are 
  of 
  use, 
  and 
  a 
  well-marked 
  difference 
  

   in 
  any 
  cue 
  character 
  is, 
  in 
  my 
  opinion, 
  a 
  sufficient 
  justification 
  for 
  a 
  distinct 
  specific 
  

   name. 
  This, 
  of 
  course, 
  necessitates 
  a 
  good 
  many 
  specific 
  names, 
  but 
  it 
  is 
  better 
  to 
  

   have 
  too 
  many 
  than 
  too 
  few, 
  and 
  so 
  long 
  as 
  each 
  form 
  is 
  properly 
  described 
  increase 
  

   of 
  species 
  only 
  adds 
  to 
  our 
  knowledge, 
  while 
  the 
  merging 
  of 
  many 
  forms 
  under 
  one 
  

   name 
  makes 
  hopeless 
  confusion, 
  for 
  the 
  author 
  who 
  does 
  so 
  seldom 
  thinks 
  it 
  

   necessary 
  to 
  give 
  an 
  adequate 
  description 
  of 
  each 
  variety 
  and 
  it 
  then 
  becomes 
  

   impossible 
  to 
  sort 
  them 
  out 
  and 
  to 
  determine 
  which 
  is 
  really 
  the 
  type 
  of 
  the 
  

   species. 
  

  

  The 
  term 
  species 
  is, 
  as 
  I 
  understand 
  it, 
  a 
  purely 
  arbitrary 
  one, 
  meaning 
  simply 
  

   an 
  assemblage 
  of 
  individuals 
  more 
  or 
  less 
  resembling 
  one 
  another 
  and 
  presumably 
  

   descended 
  from 
  a 
  common 
  parent, 
  but 
  whether 
  a 
  particular 
  individual 
  belongs 
  

   to 
  a 
  particular 
  species 
  or 
  not 
  is 
  a 
  question 
  which 
  each 
  observer 
  must 
  decide 
  for 
  

   himsQlf.f 
  

  

  * 
  Proceedings 
  of 
  the 
  Linnean 
  Society 
  of 
  New 
  South 
  Wales, 
  Vol. 
  IX., 
  part 
  4, 
  p. 
  1089. 
  

  

  t 
  "Ficm 
  these 
  remarks 
  it 
  will 
  be 
  seen 
  that 
  I 
  look 
  at 
  the 
  term 
  species 
  as 
  one 
  arbitrarily 
  given, 
  for 
  the 
  sake 
  of 
  

   convenience, 
  to 
  a 
  set 
  of 
  individuals 
  closely 
  resembling 
  each 
  other, 
  and 
  that 
  it 
  does 
  not 
  essentially 
  differ 
  from 
  the 
  terra 
  

   variety, 
  which 
  is 
  given 
  to 
  less 
  distinct 
  and 
  more 
  fluctuating 
  forms. 
  The 
  term 
  variety, 
  again, 
  in 
  comparison 
  with 
  mere 
  

   individual 
  differences, 
  is 
  also 
  applied 
  arbitrarily, 
  for 
  convenience' 
  sake."— 
  Darwin, 
  " 
  Origin 
  of 
  Species," 
  Ed. 
  VI., 
  p. 
  42. 
  

  

  