﻿18 
  A 
  MONOGRAPH 
  OF 
  THE 
  VICTORIAN 
  SPONGES. 
  

  

  described 
  above, 
  the 
  nucleolus 
  itself 
  lialf 
  in 
  and 
  half 
  out 
  of 
  the 
  nucleus, 
  and 
  this 
  

   fact 
  supports 
  the 
  supposition 
  that 
  the 
  granules 
  of 
  the 
  outer 
  protoplasm 
  may 
  under 
  

   certain 
  circumstances 
  pass 
  through 
  the 
  nuclear 
  membrane 
  (in 
  the 
  opposite 
  direction 
  

   to 
  that 
  in 
  which 
  the 
  nucleolus 
  appeared 
  to 
  be 
  travelhng). 
  Another 
  feature 
  of 
  

   considerable 
  interest 
  in 
  the 
  ova 
  of 
  Leucosnleiiia 
  depressa 
  is 
  the 
  presence 
  in 
  the 
  

   nucleus 
  of 
  distinct 
  traces 
  of 
  a 
  nuclear 
  network, 
  composed 
  of 
  very 
  delicate, 
  branching 
  

   and 
  anastomosing 
  threads, 
  which 
  seem 
  to 
  stain 
  more 
  darkly 
  than 
  the 
  surrounding 
  

   protoplasm, 
  and 
  appear 
  somewhat 
  as 
  shown 
  in 
  tlie 
  figure. 
  

  

  These 
  examples 
  may 
  suffice 
  to 
  illustrate 
  the 
  structure 
  of 
  the 
  ovum 
  of 
  the 
  

   Calcarea 
  Homoccela, 
  and 
  indeed, 
  of 
  calcareous 
  sponges 
  in 
  general.* 
  Although 
  the 
  

   adult 
  sponge 
  is 
  generally 
  admitted 
  to 
  be 
  amongst 
  the 
  simplest 
  and 
  most 
  lowly 
  of 
  

   organisms, 
  the 
  ovnm 
  appears 
  to 
  be 
  possessed 
  of 
  a 
  complexity 
  of 
  structure 
  far 
  beyond 
  

   what 
  might 
  be 
  expected, 
  and 
  this 
  complexity 
  appears 
  especially 
  to 
  concern 
  the 
  

   nucleus. 
  

  

  Such 
  then 
  are 
  the 
  various 
  cell 
  -elements 
  which 
  take 
  part 
  in 
  the 
  formation 
  of 
  the 
  

   • 
  mesoderm 
  of 
  the 
  Calcarea 
  Homoccela, 
  but 
  in 
  addition 
  to 
  these 
  there 
  occur 
  in 
  the 
  

   mesoderm 
  of 
  Leucosolenia 
  cavata 
  a 
  great 
  number 
  of 
  bodies 
  whose 
  nature 
  is 
  still 
  a 
  

   matter 
  of 
  conjecture, 
  but 
  which 
  may 
  be 
  conveniently 
  described 
  in 
  this 
  place. 
  

  

  Yellow 
  Granules. 
  — 
  The 
  bodies 
  in 
  question 
  lie 
  embedded 
  in 
  large 
  numbers 
  

   and 
  grouped 
  at 
  fairly 
  regular 
  intervals 
  in 
  the 
  mesoderm 
  beneath 
  the 
  layer 
  

   of 
  collared 
  cells 
  (PL 
  VI., 
  Figs. 
  4 
  and 
  5); 
  they 
  consist 
  of 
  spherical 
  granules 
  (perhaps 
  

   small 
  cells), 
  mostly 
  aggregated 
  in 
  very 
  definite 
  clusters 
  and 
  each 
  with 
  a 
  dark 
  

   spot 
  in 
  its 
  centre 
  (nucleus 
  ?). 
  The 
  arrangement 
  of 
  the 
  granules 
  in 
  each 
  aggregation 
  

   is 
  peculiar 
  and 
  characteristic. 
  First 
  they 
  may 
  be 
  arranged 
  in 
  a 
  solid 
  heap 
  

   of 
  comparatively 
  small 
  size, 
  about 
  0-025 
  mm. 
  in 
  diameter. 
  This 
  appears 
  

   to 
  be 
  an 
  immature 
  condition 
  (PI. 
  VI., 
  Fig. 
  5). 
  Sometimes 
  there 
  appears 
  in 
  such 
  

   a 
  heap 
  a 
  darl; 
  area 
  resembling 
  a 
  nucleus, 
  which 
  seems 
  to 
  indicate 
  that 
  the 
  wdiole 
  mass 
  

   of 
  granules 
  may 
  be 
  origmally 
  a 
  single 
  nucleated 
  cell. 
  Then 
  the 
  granules, 
  each 
  

   about 
  0'0023 
  mm. 
  in 
  diameter, 
  appear 
  to 
  spread 
  themselves 
  out, 
  so 
  that 
  in 
  the 
  next 
  

   stage, 
  which 
  I 
  regard 
  as 
  the 
  more 
  advanced 
  condition, 
  they 
  form 
  a 
  ring 
  surrounding 
  

   an 
  empty, 
  discoid 
  or 
  sometimes 
  crescentic 
  space 
  (PI. 
  VI., 
  Fig. 
  5). 
  One 
  side 
  of 
  the 
  

   ring 
  appears 
  to 
  be 
  always 
  thicker 
  {i.e.^ 
  composed 
  of 
  more 
  granules) 
  than 
  the 
  other, 
  

   which 
  may 
  be 
  composed 
  of 
  only 
  a 
  single 
  row 
  of 
  granules. 
  The 
  diameter 
  of 
  this 
  

   annular 
  aggregation 
  of 
  small 
  cells 
  or 
  granules 
  is 
  about 
  0'034 
  mm. 
  

  

  * 
  For 
  further 
  particulars 
  as 
  to 
  the 
  ova 
  of 
  sponges 
  vide 
  Dendy, 
  " 
  Studies 
  on 
  the 
  Comparative 
  Anatomj' 
  of 
  Sponges," 
  

   III. 
  and 
  IV., 
  loc. 
  cit. 
  

  

  