﻿16 
  A 
  MONOGRAPH 
  OF 
  THE 
  VICTORIAN 
  SPONGES. 
  

  

  The 
  ova, 
  on 
  the 
  other 
  hand, 
  are 
  easily 
  recognisable, 
  and 
  frequently 
  met 
  with 
  in 
  

   preparations. 
  Tigiire 
  4, 
  Plate 
  YI., 
  for 
  example, 
  shows 
  an 
  ovmn 
  of 
  Leucosolenia 
  cavata, 
  

   lying 
  in 
  the 
  gelatinous 
  gromid-siibstance 
  of 
  the 
  mesoderm 
  beneath 
  the 
  la5-er 
  of 
  

   collared 
  cells. 
  This 
  ovnm 
  is 
  simply 
  a 
  very 
  large 
  amoeboid 
  cell, 
  about 
  0.025 
  mm. 
  in 
  

   its 
  longer 
  diameter, 
  with 
  an 
  oval 
  form 
  and 
  a 
  very 
  distinct 
  nucleus 
  about 
  0-006 
  mm. 
  in 
  

   diameter. 
  The 
  nucleus 
  is 
  granular, 
  and 
  stains 
  (in 
  this 
  case) 
  more 
  deeply 
  than 
  the 
  

   surrounding 
  protoplasm, 
  which 
  is 
  also 
  granular. 
  Around 
  this 
  ovum 
  are 
  congregated 
  

   a 
  number 
  of 
  other 
  mesodermal 
  cells 
  (probably 
  amoeboid) 
  of 
  much 
  smaller 
  size. 
  These 
  

   are 
  probably 
  the 
  commencement 
  of 
  the 
  characteristic 
  capsule 
  which 
  seems 
  generally 
  

   to 
  surround 
  the 
  developing 
  embryo 
  of 
  calcareous 
  sponges. 
  Possibly 
  the 
  particular 
  

   ovum 
  here 
  described 
  is 
  not 
  adult, 
  for 
  it 
  does 
  not 
  present 
  quite 
  the 
  characteristic 
  

   appearance 
  of 
  a 
  ripe 
  calcisponge 
  ovum. 
  

  

  In 
  a 
  specimen 
  of 
  Leucosolenia 
  pellicnlnta, 
  however, 
  I 
  found 
  very 
  numerous 
  

   mature 
  ova 
  of 
  much 
  more 
  characteristic 
  structure, 
  and 
  these 
  may 
  be 
  taken 
  as 
  a 
  type 
  

   for 
  the 
  whole 
  group. 
  In 
  this 
  species 
  the 
  wall 
  of 
  the 
  Ascon-tube 
  is 
  very 
  thin, 
  and 
  the 
  

   mesoderm 
  is 
  but 
  feebly 
  developed. 
  The 
  mature 
  ova, 
  on 
  the 
  other 
  hand, 
  are 
  very 
  

   large, 
  their 
  shorter 
  diameter 
  measuring 
  two 
  or 
  three 
  times 
  the 
  thickness 
  of 
  the 
  wall 
  

   of 
  the 
  tube. 
  Hence, 
  Avherever 
  an 
  ovum 
  occurs, 
  the 
  tube-wall 
  is 
  swollen 
  out, 
  and 
  the 
  

   swelling 
  always 
  projects 
  inwards, 
  into 
  the 
  gastral 
  cavity, 
  and 
  not 
  outwards, 
  for 
  the 
  

   ovum 
  lies 
  inside 
  the 
  layer 
  of 
  rigid 
  spicules 
  composing 
  the 
  skeleton 
  of 
  the 
  sponge. 
  

   Hence 
  the 
  layer 
  of 
  collared 
  cells 
  lining 
  the 
  gastral 
  cavity 
  is 
  lifted 
  up 
  into 
  a 
  mound-hke 
  

   swelling 
  over 
  each 
  ovum, 
  exactly 
  as 
  I 
  have 
  described 
  in 
  the 
  case 
  of 
  the 
  developing 
  

   embryos 
  of 
  Grantin 
  labyrinthica.* 
  Moreover, 
  the 
  ovum 
  already 
  lies 
  in 
  a 
  distinct 
  

   cavity 
  lined 
  by 
  a 
  delicate 
  endothelial 
  membrane 
  just 
  like 
  the 
  embryo 
  capsule 
  of 
  

   Sycandra 
  raphanus 
  or 
  Grantia 
  labyrinthica. 
  

  

  The 
  ovum 
  itself 
  (Pl.VIII., 
  Fig. 
  7) 
  is 
  usually 
  irregularly 
  oval 
  in 
  longitudinal 
  section, 
  

   flattened 
  on 
  the 
  side 
  which 
  lies 
  next 
  to 
  the 
  spicules 
  and 
  swollen 
  out 
  on 
  the 
  other. 
  It 
  

   measures 
  about 
  0-085 
  mm. 
  in 
  longest 
  diameter. 
  The 
  nucleus 
  is 
  very 
  large,^ 
  and 
  its 
  shape 
  

   appears 
  to 
  follow 
  that 
  of 
  the 
  ovimi 
  to 
  which 
  it 
  belongs; 
  its 
  longer 
  diameter 
  measures 
  

   about 
  0-042 
  mm. 
  in 
  length 
  ; 
  it 
  lies 
  pretty 
  nearly 
  in 
  the 
  centre 
  of 
  the 
  ovum. 
  There 
  

   is 
  always 
  one 
  very 
  large 
  spherical 
  nucleolus 
  whose 
  position 
  in 
  the 
  nucleus 
  varies. 
  It 
  

   lies 
  sometimes 
  towards 
  one 
  end, 
  sometimes 
  to 
  the 
  side, 
  and 
  in 
  one 
  case 
  I 
  distinctly 
  

   saw 
  the 
  nucleolus 
  lying 
  half 
  inside 
  the 
  nucleus 
  and 
  lialf 
  in 
  the 
  surrounding 
  proto- 
  

   plasm. 
  The 
  nucleolus 
  is 
  about 
  0-01 
  mm. 
  in 
  diameter. 
  With 
  regard 
  to 
  the 
  more 
  

   minute 
  structure 
  of 
  these 
  different 
  parts 
  of 
  the 
  ovum 
  we 
  must 
  notice 
  that 
  the 
  body 
  of 
  

   the 
  ovum 
  {i.e., 
  the 
  part 
  outside 
  the 
  nucleus) 
  is 
  a 
  naked 
  mass 
  of 
  coarsely 
  granular 
  

   protoplasm 
  which 
  stains 
  very 
  deeply. 
  The-nucleus 
  is 
  enclosed 
  in 
  a 
  very 
  distinct 
  

  

  Victori'a 
  'j^g° 
  *^^ 
  Jl^''"'''^8astrula 
  Stage 
  in 
  the 
  Development 
  of 
  Calcareous 
  Sponges." 
  Proceedings 
  of 
  the 
  Royal 
  Society 
  of 
  

  

  