﻿Structure 
  of 
  AstpwEospongia 
  meniscus. 
  115 
  

  

  branches. 
  Besides 
  these, 
  there 
  are 
  numerous 
  smaller 
  open- 
  

   ings, 
  each 
  having 
  the 
  characteristic 
  stellate 
  appearance. 
  

  

  The 
  branches 
  of 
  the 
  star 
  themselves 
  are 
  made 
  up 
  of 
  smaller 
  

   beads, 
  gradually 
  decreasing 
  in 
  size 
  as 
  they 
  approach 
  the 
  point, 
  

   each 
  of 
  these 
  beads 
  being 
  formed 
  similarly 
  to 
  the 
  central 
  cell, 
  

   namely, 
  being 
  furnished 
  with 
  six 
  principal 
  stellate 
  pores^ 
  sur- 
  

   rounded 
  by 
  smaller 
  ones 
  which 
  give 
  to 
  the 
  arms 
  a 
  lined 
  or 
  

   striated 
  appearance. 
  The 
  stellate 
  pores 
  only 
  appear 
  under 
  a 
  

   magnifying 
  power 
  of 
  about 
  three 
  hundred 
  diameters. 
  

  

  Commencing 
  in 
  the 
  central 
  bead 
  and 
  traceable 
  throughout 
  

   the 
  line 
  of 
  cells 
  forming 
  the 
  arms 
  of 
  the 
  star, 
  is 
  a 
  tube 
  or 
  spine 
  

   connecting 
  each 
  with 
  the 
  other, 
  the 
  final 
  point 
  appearing 
  open 
  

   for 
  external 
  communication. 
  

  

  A 
  yellowish 
  mineral 
  substance, 
  mostly 
  alumina, 
  surrounds 
  

   the 
  stars 
  and 
  seems 
  to 
  have 
  been 
  the 
  skin 
  or 
  epitheca. 
  

  

  Under 
  a 
  high 
  magnifying 
  power, 
  this 
  also 
  exhibits 
  the 
  

   stellate 
  pores, 
  richly 
  interlaced 
  and 
  crossed 
  by 
  fine 
  spines. 
  

   These 
  spines, 
  by 
  the 
  use 
  of 
  the 
  polariscope, 
  we 
  conclude 
  to 
  be 
  

   silicious 
  in 
  their 
  composition, 
  as 
  they 
  show 
  the 
  characteristic 
  

   bright 
  iridescence 
  indicating 
  quartz. 
  

  

  Upon 
  placing 
  one 
  of 
  the 
  specimens 
  in 
  very 
  dilute 
  acid 
  this 
  

   yellow 
  material, 
  still 
  retaining 
  its 
  form, 
  floats 
  like 
  a 
  thin 
  mem- 
  

   brane 
  attached 
  to 
  the 
  fossil. 
  This 
  fact 
  can 
  only 
  be 
  explained 
  

   by 
  the 
  great 
  number 
  of 
  spines 
  which 
  thus 
  contribute 
  to 
  its 
  

   tenacity, 
  and 
  these 
  spines 
  bear 
  the 
  greatest 
  resemblance 
  to 
  those 
  

   figured 
  by 
  Dr. 
  Bronn 
  in 
  his 
  " 
  Thier 
  Reichs" 
  (Table 
  1, 
  fig. 
  12). 
  

  

  The 
  manner 
  of 
  growth 
  has 
  already 
  been 
  indicated 
  in 
  the 
  

   description 
  of 
  the 
  star, 
  and 
  it 
  appears 
  to 
  be 
  by 
  the 
  gradual 
  

   development 
  and 
  division 
  of 
  a 
  single 
  cell. 
  

  

  Taking 
  for 
  example 
  a 
  single 
  star 
  for 
  a 
  basis 
  and 
  counting 
  six 
  

   larger 
  cells 
  to 
  each 
  branch 
  we 
  have 
  thirty-six 
  cells, 
  and 
  the 
  

   central 
  or 
  germinating 
  bead 
  of 
  these 
  branches 
  would 
  make 
  

   thirty-seven 
  cells 
  ; 
  each 
  of 
  these 
  with 
  an 
  innate 
  power 
  of 
  repro- 
  

   duction 
  by 
  elongation, 
  could 
  produce, 
  if 
  necessary, 
  another 
  

   mother 
  cell 
  Which 
  in 
  its 
  turn 
  could 
  throw 
  off 
  six 
  branches 
  and 
  

   so 
  on 
  till 
  the 
  necessities 
  of 
  the 
  sponge 
  were 
  accomplished 
  and 
  

   its 
  growth 
  attained. 
  

  

  But 
  as 
  a 
  rule 
  the 
  general 
  growth 
  would 
  seem 
  to 
  indicate 
  that 
  

   the 
  function 
  of 
  germination 
  was 
  confined 
  to 
  the 
  central 
  cell. 
  

  

  