﻿A 
  MONOGRAPH 
  OF 
  THE 
  VICTORIAN 
  SPONGES. 
  15 
  

  

  diameter, 
  and 
  stain 
  deeply, 
  but 
  the 
  actual 
  outlines 
  of 
  the 
  cells 
  I 
  have 
  not 
  been 
  able 
  to 
  

   distinguish. 
  The 
  collared 
  cells 
  of 
  the 
  endoderm 
  are 
  not 
  continued 
  over 
  this 
  sheath, 
  

   but, 
  as 
  shown 
  in 
  PI. 
  VI., 
  Figs. 
  1, 
  2, 
  cease 
  abruptly 
  around 
  its 
  base. 
  These 
  structures 
  

   must 
  not 
  be 
  confounded 
  with 
  the 
  ordinary 
  " 
  spicule 
  sheath 
  " 
  always 
  found 
  investing 
  

   Calcareous 
  sponge-spicules 
  (vide 
  supra). 
  The 
  latter 
  has 
  been 
  shown 
  by 
  Hteckel* 
  to 
  

   be 
  simply 
  a 
  concentration 
  of 
  the 
  gelatinous 
  ground-substance 
  immediately 
  

   surrounding 
  the 
  spicule, 
  and 
  has 
  no 
  cellular 
  structure. 
  

  

  The 
  origin 
  of 
  the 
  cellular 
  spicule 
  sheaths 
  is 
  open 
  to 
  debate. 
  I 
  prefer 
  at 
  present 
  

   to 
  regard 
  them 
  as 
  mesodermal 
  structures, 
  but, 
  on 
  the 
  other 
  hand, 
  there 
  is 
  nothing 
  to 
  

   prove 
  that 
  they 
  are 
  not 
  endodermal. 
  If, 
  however, 
  they 
  are 
  endodermal 
  then 
  Lenden- 
  

   feld's 
  emended 
  diagnosis 
  of 
  the 
  Homoccela 
  as 
  " 
  Calcispongia3 
  the 
  entoderm 
  of 
  which 
  

   consists 
  throughout 
  of 
  frilled 
  flagellate 
  cells,"! 
  will 
  no 
  longer 
  hold 
  good. 
  The 
  spicules 
  

   themselves 
  are 
  certainly 
  mesodermal 
  in 
  origin, 
  and 
  if 
  they 
  can 
  penetrate 
  through 
  the 
  

   endoderm 
  what 
  is 
  to 
  prevent 
  them 
  from 
  carrying 
  with 
  them 
  an 
  investment 
  of 
  

   mesodermal 
  cells 
  ? 
  Probably 
  these 
  cells 
  are 
  really 
  calcoblasts, 
  which 
  secrete 
  constant 
  

   additions 
  of 
  carbonate 
  of 
  lime 
  whereby 
  tlie 
  spicule 
  is 
  enabled 
  to 
  maintain 
  its 
  growth. 
  

   It 
  is 
  not 
  certain 
  which 
  of 
  the 
  mesodermal 
  cells, 
  as 
  a 
  general 
  rule, 
  function 
  as 
  

   calcoblasts 
  {i.e., 
  secrete 
  the 
  spicules), 
  but 
  I 
  have 
  elsewhere 
  given 
  it 
  as 
  my 
  opinion 
  

   that 
  the 
  ordinary 
  stellate 
  connective 
  tissue 
  cells 
  do 
  the 
  greater 
  part 
  of 
  the 
  work.]; 
  

  

  (5.) 
  The 
  next 
  mesodermal 
  elements 
  of 
  which 
  we 
  have 
  to 
  speak 
  are 
  the 
  

   Reproductive 
  Cells. 
  Schulze,§ 
  Polejaeff,|| 
  and 
  others 
  have 
  shown 
  that 
  the 
  ova 
  and 
  

   spermatozoa 
  in 
  Calcareous 
  (and, 
  indeed, 
  other) 
  sponges 
  develop 
  in 
  the 
  mesoderm, 
  and 
  

   are 
  formed 
  directly 
  from 
  the 
  amoeboid 
  cells 
  (" 
  Wanderzcllen"). 
  The 
  ovum 
  is 
  formed 
  

   simply 
  by 
  increase 
  in 
  volume 
  of 
  the 
  amoeboid 
  cell 
  and 
  the 
  si)ermatozoon 
  by 
  a 
  process 
  

   of 
  fission 
  ; 
  for 
  further 
  details 
  of 
  these 
  processes, 
  I 
  must 
  refer 
  to 
  the 
  works 
  of 
  

   Schulze 
  and 
  Polejaeff 
  just 
  quoted. 
  

  

  The 
  spermatozoa 
  I 
  have 
  not 
  seen, 
  at 
  any 
  rate 
  in 
  the 
  Calcarea 
  Homoccela, 
  but 
  we 
  

   may 
  assume 
  that 
  they 
  resemble 
  more 
  or 
  less 
  closely 
  those 
  described 
  by 
  Polejaeff 
  in 
  

   Sycandra 
  raphaiius, 
  consisting 
  of 
  a 
  very 
  minute 
  spherical 
  head 
  and 
  a 
  very 
  long 
  and 
  

   slender 
  tail 
  (0-03 
  mm. 
  long). 
  

  

  * 
  " 
  Die 
  Kalkscliwiimme." 
  

  

  I 
  Proceedings 
  of 
  tlie 
  Linnean 
  Society 
  of 
  Now 
  South 
  Wtiles, 
  Vol. 
  IX., 
  Pint 
  t, 
  p. 
  lOtHS. 
  

  

  I 
  In 
  my 
  memoir 
  on 
  tlio 
  Anatomy 
  of 
  Omiitia 
  Idliiiriiilhica 
  (loc.cit. 
  siiprH) 
  1 
  have 
  jnoposed 
  to 
  ilistinguisli 
  between 
  two 
  

   kinds 
  of 
  sjiicule-stjcrt'ting 
  cells, 
  or 
  ciilcolilasts, 
  in 
  tlie 
  Calcnrooiis 
  sponges, 
  \iy..,primai!/ 
  ctilcobhiiit!:, 
  within 
  which 
  tlie 
  spicnles 
  

   take 
  their 
  oritjin 
  as 
  in 
  mother 
  cells, 
  and 
  nccomttinj 
  i-iilcolilust.f, 
  which 
  add 
  successive 
  layers 
  of 
  carbonate 
  of 
  lime 
  to 
  the 
  

   spiculi! 
  after 
  it 
  has 
  onoi- 
  been 
  formed. 
  I 
  am 
  not 
  aware 
  that 
  anyone 
  has 
  ever 
  yet 
  seen 
  a 
  primary 
  caleoblast, 
  but 
  their 
  

   existence 
  is 
  run<lered 
  i)rol)al)le 
  by 
  the 
  analoKy 
  of 
  siliceous 
  sponges, 
  in 
  which 
  the 
  smaller 
  spicules 
  are 
  often 
  seen 
  withni 
  

   mother 
  cells 
  (prinuiry 
  silicoblasts). 
  The 
  ordinary 
  stellate 
  connective 
  tissue 
  cells, 
  or 
  some 
  of 
  them, 
  probably 
  function 
  as 
  

   secondary 
  calcoblasts, 
  as 
  also 
  do 
  the 
  endothelial 
  cells 
  ensheathing 
  the 
  rays 
  of 
  spicules 
  which 
  project 
  into 
  the 
  gastral 
  

   cavity. 
  

  

  S 
  " 
  Ueber 
  den 
  Ban 
  uiul 
  die 
  Kntwicklung 
  von 
  Siicniidni 
  idiihannn 
  Ila'ckel." 
  Zeitschrift 
  f. 
  wissenseh. 
  ZoolO(?ie. 
  

   Vol. 
  XXV. 
  Suppl. 
  

  

  l; 
  "Uber 
  das 
  S|)i'rma 
  und 
  die 
  Hpermatogenese 
  bei 
  Siicaiidii 
  ni/)/i(iHl<n 
  Hieckel." 
  (•• 
  Aus. 
  dem 
  lAWVl. 
  Dando 
  der 
  

   Sitzb. 
  tier 
  k. 
  Akad. 
  der 
  Wissenseh., 
  1 
  Abth. 
  Nov. 
  - 
  lleft, 
  Juhrg., 
  ia8'2.") 
  

  

  