﻿A 
  MONOGRAPH 
  OF 
  THE 
  VICTORIAN 
  SPONGES. 
  7 
  

  

  knowledge 
  of 
  this 
  class 
  of 
  Ccelenterata. 
  Employing 
  new 
  methods 
  of 
  histological 
  

   examination, 
  he 
  discovered 
  on 
  the 
  sm-face 
  of 
  many 
  sponges 
  a 
  delicate 
  external 
  

   pavemeiit-epitheliimi 
  not 
  hitherto 
  observed, 
  and 
  deduced 
  from 
  this 
  observation 
  the 
  

   following 
  important 
  conclusions 
  :^ 
  

  

  " 
  The 
  body 
  of 
  the 
  sponges 
  is 
  originally 
  composed 
  not 
  of 
  two, 
  but 
  of 
  three 
  

   primitive 
  cell-layers, 
  corresponding 
  to 
  those 
  which 
  m 
  the 
  higher 
  organised 
  Metazoa 
  

   are 
  called 
  exoderm, 
  mesoderm 
  and 
  entoderm. 
  The 
  exoderm 
  (or 
  outer 
  layer 
  covering 
  

   the 
  external 
  faces) 
  and 
  the 
  entoderm 
  (or 
  inner 
  layer 
  lining 
  the 
  canal-system 
  internally) 
  

   are 
  tAvo 
  simple 
  epithelial 
  plates, 
  and 
  between 
  them 
  is 
  enclosed 
  the 
  mesoderm 
  (or 
  the 
  

   middle 
  layer) 
  ; 
  this 
  latter 
  is 
  a 
  kind 
  of 
  connective 
  tissue, 
  and 
  produces 
  not 
  only 
  the 
  

   skeleton, 
  but 
  also 
  the 
  sexual 
  cells 
  (eggs 
  and 
  sperm). 
  

  

  " 
  The 
  conception 
  of 
  the 
  sponge-tissues 
  given 
  by 
  F. 
  E. 
  Schulze 
  is 
  now 
  generally 
  

   accepted, 
  and 
  it 
  is 
  very 
  probable 
  that 
  it 
  has 
  general 
  value, 
  though 
  it 
  was 
  not 
  possible 
  

   to 
  demonstrate 
  clearly 
  in 
  all 
  sponges 
  the 
  delicate 
  exodermal 
  epithelium.' 
  

  

  "* 
  

  

  The 
  Calcispongc 
  in 
  which 
  Schulze 
  discovered 
  the 
  ectodermal 
  epithelium 
  was 
  

   Sycandra 
  raphanus, 
  one 
  of 
  the 
  Heteroccsla. 
  It 
  was 
  of 
  course 
  tolerably 
  safe 
  to 
  assume 
  

   that 
  a 
  similar 
  ectodermal 
  layer 
  exists 
  also 
  in 
  the 
  Honiocccla, 
  but 
  I 
  am 
  not 
  aware 
  that 
  

   this 
  has 
  hitherto 
  been 
  definitely 
  proved. 
  Polejaeff,t 
  indeed, 
  gives 
  a 
  figure 
  of 
  a 
  section 
  

   of 
  Leucosolciiia 
  poterimn 
  in 
  which 
  what 
  are 
  evidently 
  intended 
  for 
  ectodermal 
  cells 
  

   appear, 
  but 
  the 
  figure 
  is 
  very 
  diagrammatic, 
  and 
  there 
  appears 
  to 
  be 
  no 
  mention 
  of 
  

   the 
  ectodermal 
  cells 
  anywhere 
  in 
  the 
  letterpress. 
  

  

  As 
  a 
  matter 
  of 
  fact 
  I 
  find 
  that 
  the 
  ectoderm 
  of 
  the 
  Homocoela 
  agrees 
  precisely 
  

   with 
  wliat 
  Schulze 
  has 
  described 
  for 
  Sycandra 
  raphauiis, 
  and 
  what 
  I 
  myself 
  found 
  and 
  

   described 
  in 
  Grantia 
  labyrinthica.[ 
  Except 
  in 
  the 
  case 
  of 
  very 
  well 
  preserved 
  speci- 
  

   mens 
  it 
  is 
  a 
  matter 
  of 
  great 
  difiiculty 
  to 
  make 
  out 
  satisfactorily 
  the 
  structure 
  of 
  the 
  

   ectodermal 
  epithelium. 
  In 
  cases, 
  however, 
  where 
  the 
  specimen 
  has 
  been 
  at 
  once 
  

   immersed 
  in 
  a 
  sufficient 
  quantity 
  of 
  strong 
  spirit 
  and 
  the 
  sections 
  carefully 
  prepared 
  

   by 
  means 
  of 
  the 
  paraffin 
  method, 
  care 
  being 
  taken 
  to 
  avoid 
  overheating, 
  the 
  ectoderm 
  

   generally 
  a})pears 
  in 
  section 
  as 
  a 
  delicate 
  but 
  sharp 
  outline 
  with 
  a 
  moniliform 
  or 
  

   beaded 
  appearance 
  due 
  to 
  the 
  swelling 
  caused 
  by 
  tlie 
  presence 
  of 
  the 
  nucleus 
  in 
  the 
  

   centre 
  of 
  each 
  cell. 
  In 
  my 
  sections 
  of 
  Leucosoleiiia 
  ivilsoiii, 
  n. 
  sp., 
  for 
  example, 
  I 
  

   found 
  the 
  ectoderm 
  unusually 
  well 
  preserved. 
  In 
  sections 
  vertical 
  to 
  the 
  plane 
  of 
  its 
  

   extension 
  it 
  i)resented 
  the 
  appearance 
  described 
  above 
  (IM. 
  VII., 
  Eigs. 
  2, 
  i\), 
  but 
  

   where 
  it 
  happened 
  to 
  be 
  cut 
  tangential!}', 
  or 
  sliced 
  off, 
  its 
  tiue 
  characU-r 
  could 
  

   readily 
  be 
  seen 
  (PI. 
  VII., 
  Fig. 
  4). 
  It 
  consists 
  of 
  thin, 
  llattencd, 
  plate-like 
  cells, 
  

  

  * 
  Ilri)()it 
  on 
  tliu 
  DociJ-Sca 
  Koiatosa 
  of 
  tlic 
  "Clialloiiger 
  " 
  Expeilition, 
  p. 
  l.'J. 
  

   I 
  Kcpoit 
  on 
  tlie 
  Calcarea 
  of 
  Ibe 
  " 
  CliallcnKor 
  " 
  Expedition, 
  Plnte 
  '.i, 
  Fig. 
  1. 
  

  

  ; 
  " 
  Studies 
  on 
  tlie 
  Conipaiativo 
  Anatomy 
  of 
  Sponges, 
  III.— 
  On 
  the 
  Anatomy 
  of 
  Oniiitiit 
  lahyrinthku, 
  Carti'r, 
  and 
  the 
  

   BO-catled 
  Family 
  Teichonidu." 
  Qiiaiterly 
  Journal 
  of 
  Rlicioscopical 
  Science, 
  January, 
  1891. 
  

  

  