﻿THE 
  MAIOTIO 
  PHASE 
  IN 
  ANIMALS 
  AND 
  PLANTS. 
  525 
  

  

  favourable 
  for 
  study, 
  inasmuch 
  as, 
  like 
  Fossombrouia, 
  the 
  

   lobes 
  are 
  not 
  much 
  extended 
  in 
  the 
  radial 
  direction, 
  as 
  is, 
  

   for 
  example, 
  the 
  case 
  in 
  Pel 
  Ha. 
  

  

  The 
  nucleus 
  occupies 
  the 
  centre 
  of 
  the 
  cell, 
  and 
  it 
  is 
  thus 
  

   surrounded 
  by, 
  and 
  enclosed 
  in, 
  cytoplasm 
  which 
  is 
  chiefly 
  

   aggregated 
  into 
  four 
  masses 
  corresponding 
  with 
  the 
  four 
  

   lobes 
  already 
  referred 
  to. 
  

  

  The 
  nucleus 
  contains 
  one 
  or 
  more 
  nucleoli, 
  and 
  at 
  this 
  

   stage 
  the 
  spirem 
  thread 
  can 
  be 
  traced 
  as 
  a 
  probably 
  con- 
  

   tinuous 
  filament 
  within 
  the 
  nuclear 
  wall. 
  

  

  The 
  early 
  contraction 
  figure 
  already 
  described 
  for 
  the 
  pre- 
  

   ceding 
  plants 
  occurs 
  here 
  also, 
  but 
  judging 
  from 
  the 
  relative 
  

   iuf 
  requeucy 
  with 
  which 
  it 
  was 
  observed, 
  it 
  appears 
  to 
  repre- 
  

   sent 
  a 
  very 
  transient 
  phase. 
  

  

  As 
  the 
  nucleus 
  begins 
  to 
  show 
  signs 
  of 
  approaching 
  mitosis, 
  

   the 
  first 
  obvious 
  change 
  is 
  seen 
  in 
  the 
  cytoplasm. 
  In 
  each 
  of 
  

   the 
  four 
  lobes 
  a 
  ceutrosphere 
  is 
  differentiated 
  (figs. 
  31-35), 
  

   and 
  sometimes 
  a 
  central 
  body 
  (centrosome) 
  could 
  be 
  dis- 
  

   tinguished 
  in 
  each. 
  The 
  centrospheres 
  when 
  formed 
  appear 
  

   to 
  exert 
  (or 
  to 
  represent 
  the 
  foci 
  of) 
  tractive 
  forces 
  acting 
  on 
  

   the 
  nucleus, 
  which 
  now 
  changes 
  its 
  form 
  and 
  becomes 
  dis- 
  

   tinctly 
  drawn 
  out, 
  so 
  that 
  an 
  angle 
  projects 
  towards 
  each 
  lobe. 
  

   Before 
  the 
  formation 
  of 
  the 
  centrospheres 
  the 
  nucleus 
  was 
  

   either 
  spherical 
  or 
  even 
  slightly 
  flattened 
  opposite 
  each 
  lobe. 
  

   These 
  facts 
  can 
  be 
  made 
  visible 
  both 
  in 
  spore-mother-cells 
  

   stained 
  in 
  bulk 
  and 
  mounted 
  in 
  glycerine, 
  although 
  of 
  coui'se 
  

   the 
  details 
  can 
  only 
  be 
  followed 
  in 
  sections. 
  When 
  sections 
  

   are 
  examined 
  only 
  three 
  lobes 
  at 
  most 
  can 
  be 
  seen 
  at 
  once, 
  

   and 
  unless 
  the 
  sections 
  are 
  fairly 
  thick 
  one 
  can 
  only 
  trace 
  

   fragments 
  of 
  the 
  whole 
  apparatus, 
  since 
  the 
  axes 
  of 
  the 
  centro- 
  

   spheres 
  and 
  spindles 
  lie 
  in 
  four 
  different 
  planes. 
  Aneura 
  

   multifida, 
  owing 
  to 
  the 
  smaller 
  size 
  of 
  its 
  spore-mother-cells, 
  

   affords 
  a 
  more 
  favourable 
  object 
  in 
  which 
  to 
  study 
  the 
  process 
  

   in 
  the 
  unsectioned 
  cell; 
  and 
  indeed 
  that 
  species, 
  together 
  

   with 
  Fossombronia 
  pusilla, 
  is 
  habitually 
  used 
  by 
  us 
  to 
  

   demonstrate 
  the 
  quadripolar 
  spindle 
  and 
  centrospheres 
  to 
  

   classes 
  of 
  students. 
  

  

  