﻿430 
  J. 
  W. 
  JENKINSON. 
  

  

  pronuclei 
  meet. 
  Although 
  eventually 
  the 
  fertilisation 
  spindle 
  

   will 
  intersect 
  the 
  egg-axis, 
  the 
  separate 
  " 
  copulation 
  " 
  paths 
  

   of 
  the 
  pronuclei 
  frequently 
  converge 
  to 
  a 
  point 
  which 
  is 
  not 
  

   actually 
  in 
  this 
  axis, 
  and 
  may 
  be 
  some 
  distance 
  away 
  from 
  it 
  ; 
  

   in 
  other 
  cases, 
  however, 
  the 
  sperm-nucleus 
  reaches 
  the 
  axis 
  

   before 
  the 
  female 
  pronucleus 
  has 
  joined 
  it. 
  In 
  this 
  latter 
  

   case 
  " 
  penetration 
  " 
  path, 
  " 
  copulation 
  " 
  path, 
  and 
  egg-axis 
  all 
  

   lie 
  in 
  one 
  plane, 
  which, 
  since 
  the 
  centrosome 
  divides 
  at 
  right 
  

   angles 
  to 
  it, 
  is 
  the 
  plane 
  of 
  the 
  first 
  furrow. 
  This 
  may 
  then 
  

   be 
  said 
  to 
  be 
  determined 
  by 
  the 
  point 
  of 
  entry 
  of 
  the 
  sperma- 
  

   tozoon. 
  When 
  the 
  point 
  in 
  which 
  the 
  pronuclei 
  meet 
  is 
  

   ex-axial, 
  the 
  plane 
  of 
  the 
  first 
  furrow 
  may 
  possibly 
  be 
  

   determined 
  by 
  the 
  "copulation" 
  path 
  alone, 
  as 
  Roux 
  has 
  

   shown 
  to 
  be 
  the 
  case 
  in 
  the 
  frog. 
  

  

  This 
  variability 
  in 
  the 
  position 
  in 
  which 
  the 
  pronuclei 
  first 
  

   meet 
  is 
  obviously 
  partly 
  due 
  to 
  the 
  variability 
  of 
  the 
  point 
  at 
  

   which 
  the 
  spermatozoon 
  enters 
  the 
  egg, 
  and 
  consequently 
  of 
  

   its 
  " 
  penetration 
  " 
  and 
  " 
  copulation 
  " 
  paths 
  ; 
  but 
  also 
  partly 
  

   to 
  variations 
  in 
  the 
  path 
  pursued 
  by 
  the 
  female 
  pronucleus, 
  

   which 
  does 
  not 
  necessarily 
  descend 
  vertically 
  from 
  the 
  animal 
  

   pole 
  towards 
  the 
  centre 
  of 
  the 
  egg, 
  but 
  may 
  diverge 
  from 
  the 
  

   egg-axis 
  (figs. 
  B. 
  and 
  C). 
  

  

  A 
  further 
  result 
  of 
  this 
  is 
  that 
  the 
  female 
  pronucleus 
  may 
  

   come 
  in 
  contact 
  with 
  the 
  sperm 
  sphere 
  at 
  any 
  point 
  on 
  its 
  

   inner 
  and 
  upper 
  surface. 
  

  

  The 
  end 
  is, 
  however, 
  always 
  the 
  same; 
  the 
  female 
  pro- 
  

   nucleus 
  enters 
  the 
  vacuolated 
  substance 
  of 
  the 
  sphere, 
  and 
  

   comes 
  to 
  lie 
  close 
  to 
  the 
  sperm-nucleus, 
  with 
  the 
  centrosome 
  

   or 
  diverging 
  centrosomes 
  between 
  the 
  two 
  (fig. 
  29), 
  the 
  line 
  

   joining 
  the 
  two 
  pronuclei 
  intersecting 
  that 
  between 
  the 
  two 
  

   centrosomes 
  at 
  right 
  angles. 
  The 
  large 
  vacuoles 
  of 
  the 
  

   sperm 
  sphere 
  are 
  thus 
  divided 
  into 
  two 
  sets, 
  one 
  adjacent 
  to 
  

   each 
  centrosome 
  (fig. 
  31). 
  These 
  two 
  sets 
  of 
  vacuoles 
  usually 
  

   appear 
  in 
  preparations 
  each 
  as 
  a 
  single 
  large 
  vacuole 
  ; 
  this 
  

   appearance 
  is 
  artificial 
  and 
  due 
  to 
  the 
  breaking 
  down 
  of 
  the 
  

   thin 
  separating 
  lamellae. 
  

  

  Although 
  it 
  seems 
  clear 
  that 
  here, 
  as 
  in 
  many 
  other 
  cases. 
  

  

  