﻿14 
  A 
  MONOGEAPH 
  OF 
  THE 
  VICTORIAN 
  SPONGES. 
  

  

  these 
  cavities 
  are 
  lined 
  by 
  a 
  single 
  layer 
  of 
  gigantic 
  pavement 
  cells 
  whose 
  function 
  

   appears 
  to 
  be 
  to 
  supply 
  the 
  growing 
  embryo 
  with 
  nourishment. 
  Polejaeff* 
  had 
  

   previously 
  called 
  attention 
  to 
  " 
  the 
  extraordinary 
  growth 
  of 
  the 
  endothelial 
  cells 
  

   surrounding 
  the 
  growing 
  embryos" 
  in 
  various 
  horny 
  sponges. 
  Schiilzef 
  long 
  since 
  

   showed 
  that 
  the 
  embryos 
  of 
  Sycandra 
  raphanus 
  lie 
  in 
  special 
  cavities 
  in 
  the 
  

   mesoderm 
  lined 
  by 
  flattened 
  pavement 
  cells, 
  and 
  I 
  have 
  found 
  the 
  same 
  thing 
  in 
  

   Grantia 
  lahyrinthica.\ 
  But 
  in 
  neither 
  of 
  these 
  two 
  cases 
  do 
  the 
  pavement 
  cells 
  of 
  

   the 
  embryo 
  capsule 
  exhibit 
  anything 
  remarkable 
  in 
  size 
  or 
  form, 
  as 
  in 
  the 
  horny 
  

   sponges 
  referred 
  to 
  above. 
  Similar 
  endothelial 
  capsules 
  occur 
  around 
  the 
  ova 
  of 
  

   Leucosolcnia 
  pelliculata, 
  but 
  do 
  not 
  require 
  further 
  description. 
  

  

  I 
  have 
  now, 
  however, 
  to 
  record 
  the 
  occurrence, 
  in 
  Leucosolenia 
  wilsoui, 
  of 
  

   embryo 
  capsules 
  composed 
  of 
  large, 
  thick, 
  plate-like 
  cells 
  resembling, 
  though 
  on 
  a 
  

   smaller 
  scale, 
  those 
  found 
  in 
  Stelospongos. 
  The 
  peculiar 
  position 
  of 
  the 
  embryos 
  in 
  

   Leucosolenia 
  wilsoni 
  will 
  be 
  described 
  later 
  on, 
  when 
  we 
  come 
  to 
  speak 
  of 
  the 
  canal 
  

   system. 
  Suffice 
  it 
  now 
  to 
  observe 
  that 
  they 
  lie 
  in 
  spherical 
  cavities 
  excavated 
  in 
  the 
  

   mesoderm. 
  The 
  cavity 
  itself 
  is 
  about 
  0*14 
  mm. 
  in 
  diameter, 
  and 
  is 
  lined 
  by 
  a 
  single 
  

   layer 
  of 
  large, 
  polygonal 
  cells 
  of 
  unusual 
  thickness 
  (PL 
  VII., 
  Fig. 
  3). 
  Each 
  cell 
  is 
  about 
  

   0-028 
  mm. 
  in 
  diameter, 
  and 
  0-009 
  mm. 
  in 
  thickness. 
  The 
  protoplasm 
  composing 
  it 
  

   is 
  highly 
  granular 
  and 
  stains 
  well. 
  The 
  nucleus 
  is 
  small 
  and 
  spherical, 
  measuring 
  

   only 
  about 
  0-005 
  mm. 
  in 
  diameter 
  ; 
  owing 
  doubtless 
  to 
  the 
  granular 
  nature 
  of 
  the 
  

   protoplasm 
  surrounding 
  it, 
  it 
  is 
  not 
  easy 
  to 
  make 
  out. 
  There 
  can 
  be 
  no 
  doubt 
  that 
  

   the 
  function 
  of 
  these 
  cells 
  is 
  to 
  supply 
  the 
  developing 
  embryo 
  with 
  nutriment, 
  but 
  I 
  

   have 
  not 
  seen 
  any 
  connection 
  between 
  them 
  and 
  the 
  ectodermal 
  cells 
  of 
  the 
  embryo 
  

   such 
  as 
  I 
  have 
  described 
  in 
  Stelospongos. 
  

  

  We 
  have 
  next 
  to 
  deal 
  with 
  the 
  endothelial 
  cells 
  which 
  ensheath 
  the 
  spicule-rays 
  

   projecting 
  into 
  the 
  gastral 
  cavity. 
  In 
  many 
  Homocoela 
  quadriradiate 
  spicules 
  are 
  

   present, 
  and 
  the 
  apical 
  ray 
  usually, 
  if 
  not 
  always, 
  projects 
  through 
  the 
  layer 
  of 
  

   collared 
  cells 
  into 
  the 
  cavity 
  of 
  the 
  Ascon-tube 
  (gastral 
  cavity). 
  Probably 
  in 
  all 
  cases 
  

   this 
  projecting 
  ray 
  is 
  not 
  naked, 
  but 
  clothed 
  by 
  an 
  investing 
  sheath 
  of 
  flattened, 
  

   plate-like, 
  nucleated 
  cells. 
  This 
  cellular 
  sheath 
  is 
  very 
  distinctly 
  shown 
  in 
  my 
  

   preparations 
  of 
  Leucosolenia 
  stolonifer 
  (PI. 
  VI., 
  Fig. 
  2), 
  and 
  again 
  in 
  Leucosolenia 
  

   tripodifera. 
  If 
  the 
  spicule 
  is 
  dissolved 
  out 
  by 
  means 
  of 
  weak 
  acid, 
  as 
  happens 
  in 
  

   staining 
  the 
  preparations 
  by 
  the 
  borax-carmine 
  method, 
  the 
  cellular 
  sheath 
  is 
  left 
  as 
  an 
  

   empty, 
  elongated, 
  conical 
  bag, 
  hanging 
  on 
  to 
  the 
  wall 
  of 
  the 
  gastral 
  cavity. 
  The 
  cells 
  

   composing 
  the 
  sheath 
  somewhat 
  resemble 
  the 
  cells 
  of 
  the 
  ectoderm, 
  and 
  are 
  arranged 
  

   like 
  them 
  in 
  a 
  single 
  layer. 
  Their 
  nuclei 
  are 
  very 
  distinct, 
  about 
  0-0034 
  mm. 
  in 
  

  

  Report 
  on 
  the 
  Keratosa 
  of 
  the 
  " 
  Challenger 
  " 
  Expedition, 
  p. 
  52. 
  

   "Ueber 
  den 
  Ban 
  und 
  die 
  Entwicklung 
  von 
  Sycandra 
  raphar 
  

  

  7. 
  Suppl. 
  

  

  I 
  " 
  Studies 
  on 
  the 
  Comparative 
  Anatomy 
  of 
  Sponges, 
  III.," 
  &c. 
  loc. 
  cit. 
  

  

  t 
  "Ueber 
  den 
  Ban 
  und 
  die 
  Entwicklung 
  von 
  Sycandra 
  raphanus 
  Hreckel." 
  Zeitschrift 
  f. 
  wissensch. 
  Zoologie, 
  

   Vol. 
  XXV. 
  Suppl. 
  

  

  