﻿A 
  MONOGRAPH 
  OF 
  THE 
  VICTORIAN 
  SPONGES. 
  17 
  

  

  nuclear 
  membrane, 
  which 
  stains 
  deeply, 
  and 
  it 
  is 
  itself 
  composed 
  of 
  a 
  much 
  more 
  

   finely 
  granular 
  material 
  which 
  stains 
  less 
  deeply 
  than 
  the 
  outside 
  protoplasm. 
  The 
  

   nucleolus 
  stains 
  more 
  deeply 
  than 
  any 
  other 
  part 
  and 
  appears 
  to 
  be 
  homogeneous 
  and 
  

   devoid 
  of 
  structure. 
  In 
  addition 
  to 
  the 
  large 
  nucleolus 
  there 
  are 
  generally 
  visible 
  in 
  

   the 
  nucleus 
  a 
  number 
  of 
  very 
  much 
  smaller 
  bodies 
  resembling 
  the 
  nucleolus 
  in 
  

   appearance, 
  but 
  it 
  is 
  doubtful 
  whether 
  they 
  have 
  really 
  the 
  same 
  composition 
  as 
  the 
  

   latter, 
  especially 
  when 
  we 
  compare 
  them 
  with 
  similar 
  bodies 
  in 
  the 
  ovum 
  of 
  Leitcoso- 
  

   lenia 
  depressa, 
  which 
  I 
  propose 
  to 
  describe 
  next. 
  

  

  In 
  my 
  only 
  specimen 
  of 
  Leucosolenia 
  depressa 
  adult 
  ova 
  are 
  extremely 
  abundant. 
  

   Like 
  the 
  embryos 
  in 
  the 
  closely 
  allied 
  species, 
  Leucosolenia 
  wilsoni, 
  the 
  ova 
  

   are 
  imbedded 
  in 
  the 
  mesodermal 
  tissue 
  which 
  in 
  part 
  blocks 
  up 
  the 
  cavities 
  of 
  the 
  

   Ascon-tubes 
  (gastral 
  cavities), 
  but 
  there 
  is 
  no 
  definite 
  layer 
  of 
  large, 
  plate-like, 
  nutritive 
  

   cells 
  around 
  each. 
  Such 
  may, 
  however, 
  be 
  formed 
  later 
  on 
  as 
  the 
  embryo 
  develops. 
  

   The 
  ova 
  are 
  of 
  great 
  size, 
  measuring 
  0"17 
  mm. 
  in 
  longer 
  diameter, 
  and, 
  as 
  is 
  

   usually 
  the 
  case 
  with 
  the 
  ova 
  of 
  the 
  same 
  sponge, 
  are 
  all 
  in 
  very 
  much 
  the 
  same 
  

   state 
  of 
  development 
  and 
  resemble 
  one 
  another 
  closely. 
  Figure 
  8, 
  Plate 
  VIII., 
  repre- 
  

   sents 
  a 
  section 
  of 
  one 
  of 
  these 
  ova. 
  The 
  outline 
  of 
  the 
  section 
  is 
  indicated 
  by 
  the 
  

   dotted 
  line 
  and, 
  to 
  save 
  labour, 
  only 
  a 
  portion 
  of 
  the 
  protoplasm 
  outside 
  the 
  nucleus 
  

   is 
  filled 
  in. 
  The 
  ova 
  vary 
  somewhat 
  in 
  shape 
  and 
  may 
  be 
  described 
  as 
  irregularly 
  

   spherical. 
  Owing 
  to 
  the 
  absence 
  of 
  spicules 
  from 
  the 
  surrounding 
  tissues 
  they 
  are 
  

   not 
  definitely 
  flattened 
  on 
  one 
  side 
  as 
  in 
  Leucosolenia 
  pelliculata. 
  The 
  nucleus 
  is 
  

   very 
  large 
  indeed, 
  0-07G 
  mm. 
  in 
  diameter, 
  and 
  approximately 
  spherical. 
  The 
  

   nucleolus 
  is 
  distinct 
  and 
  also 
  spherical, 
  0*0085 
  mm. 
  in 
  diameter. 
  Within 
  the 
  

   nucleolus 
  several 
  small, 
  highly 
  refringent 
  granules 
  are 
  visible. 
  

  

  The 
  body 
  of 
  the 
  ovum, 
  outside 
  the 
  nucleus, 
  is 
  composed 
  (principally 
  at 
  any 
  rate) 
  

   of 
  distinct, 
  closely 
  packed, 
  more 
  or 
  less 
  spherical 
  granules, 
  each 
  about 
  0-003 
  mm. 
  in 
  

   diameter 
  ; 
  the 
  whole 
  forming 
  a 
  deeply-staining 
  mass. 
  The 
  nucleus 
  is 
  composed 
  as 
  

   usual 
  of 
  a 
  very 
  finely 
  granular 
  and 
  less 
  deeply-staining 
  substance, 
  and 
  is 
  invested 
  in 
  

   a 
  very 
  distinct, 
  deeply-staining 
  membrane. 
  Just 
  inside 
  this 
  membrane, 
  and 
  for 
  the 
  

   most 
  part 
  touching 
  it, 
  lies 
  an 
  irregular 
  row 
  of 
  spherical 
  granules 
  closely 
  resembling 
  

   in 
  size 
  and 
  other 
  characters 
  the 
  granules 
  of 
  the 
  outer 
  protoplasm. 
  These 
  granules 
  

   occur 
  in 
  tlie 
  some 
  [)osition 
  with 
  great 
  constancy 
  in 
  all 
  the 
  ova, 
  and 
  form 
  a 
  character- 
  

   istic 
  and 
  conspicuous 
  feature. 
  They 
  look 
  as 
  if 
  they 
  were 
  granules 
  belonging 
  to 
  the 
  

   outer 
  protoplasm 
  which 
  have 
  actually 
  passed 
  through 
  the 
  nuclear 
  membrane. 
  

   Whether 
  this 
  passage 
  is 
  normal 
  or 
  pathological 
  (due 
  to 
  reagents) 
  I 
  know 
  not. 
  In 
  

   Leucosolenia 
  pelliculata 
  we 
  liav(> 
  ah'cady 
  seen 
  similar 
  granules, 
  but 
  they 
  are 
  not 
  

   arranged 
  with 
  anytliing 
  like 
  the 
  same 
  regularity 
  around 
  the 
  inside 
  of 
  the 
  nuclear 
  

   membrane, 
  nevertheless 
  a 
  tendency 
  towards 
  such 
  arrangement 
  may 
  somi^tiines 
  he 
  

   observed, 
  as 
  is 
  shown 
  in 
  Figure 
  7, 
  IMatcVIlT. 
  In 
  the 
  latter 
  species 
  also 
  1 
  noticed, 
  as 
  

  

  