﻿MATURATION, 
  ETC., 
  OF 
  THE 
  EGG 
  OF 
  THE 
  AXOLOTL. 
  447 
  

  

  In 
  Ascaris 
  the 
  entrance 
  takes 
  places 
  while 
  the 
  nucleus 
  of 
  

   the 
  primary 
  oocyte 
  is 
  yet 
  intact 
  ; 
  the 
  same 
  is 
  true 
  of 
  Nereis 
  

   (Wilson), 
  Myzostoma 
  (Wheeler), 
  and 
  some 
  others. 
  In 
  others 
  

   again 
  the 
  sperm 
  enters 
  during 
  some 
  stage 
  of 
  the 
  first 
  polar 
  

   spindle 
  (Ophryotrocha 
  [Korschelt], 
  Chastopterus 
  [Mead], 
  

   Physa 
  [von 
  Kostanecki] 
  , 
  Sagitta 
  [Boveri] 
  , 
  and 
  many 
  more) 
  ; 
  

   or 
  again 
  the 
  entrance 
  may 
  be 
  deferred 
  until 
  the 
  first 
  polar 
  

   body 
  has 
  been 
  extruded 
  and 
  the 
  second 
  polar 
  spindle 
  formed, 
  

   as, 
  for 
  example, 
  in 
  Amphioxus 
  (Sobotta), 
  Petromyzon 
  

   (Bohm), 
  the 
  Trout 
  (Behrens), 
  the 
  Newt 
  (Michaelis), 
  the 
  

   Mouse 
  (Sobotta), 
  and 
  the 
  Axolotl, 
  or 
  even 
  until 
  the 
  second 
  

   polar 
  body 
  also 
  has 
  been 
  given 
  off 
  (Toxopneustes 
  [Wilson, 
  

   1895], 
  Echinus 
  [Boveri], 
  Tiara 
  [Boveri, 
  1890]). 
  

  

  It 
  is 
  an 
  interesting 
  speculation 
  whether 
  in 
  the 
  cases 
  first 
  

   mentioned 
  the 
  formation 
  of 
  both 
  polar 
  bodies, 
  or 
  of 
  the 
  second 
  

   only, 
  is 
  dependent 
  on 
  the 
  entrance 
  of 
  the 
  spermatozoon. 
  

   Pick 
  has 
  surmised 
  that 
  this 
  is 
  so 
  in 
  the 
  Axolotl, 
  and 
  Mead 
  in 
  

   Chastopterus; 
  while 
  Boveri 
  makes 
  the 
  same 
  suggestion 
  for 
  the 
  

   species 
  of 
  Sagitta 
  investigated 
  by 
  him, 
  though 
  he 
  quotes 
  an 
  

   observation 
  of 
  Pol's 
  on 
  another 
  species 
  that 
  the 
  polar 
  bodies 
  

   will 
  form 
  in 
  any 
  case, 
  though 
  much 
  more 
  slowly 
  in 
  an 
  unferti- 
  

   lised 
  egg. 
  With 
  this 
  may 
  be 
  compared 
  Hill's 
  statement 
  that 
  

   in 
  Phallusia 
  the 
  formation 
  of 
  the 
  polar 
  bodies 
  is 
  independent 
  

   of 
  fecundation. 
  

  

  That 
  an 
  immediate 
  change 
  is 
  wrought 
  in 
  the 
  cytoplasm 
  of 
  

   the 
  egg 
  by 
  the 
  entrance 
  of 
  the 
  spermatozoon 
  is 
  proved 
  by 
  an 
  

   interesting 
  experiment 
  of 
  Ziegler's, 
  in 
  which 
  the 
  egg 
  is 
  

   divided 
  into 
  two 
  pieces, 
  one 
  containing 
  the 
  egg 
  nucleus, 
  the 
  

   other 
  the 
  sperm 
  and 
  centrosome. 
  The 
  latter 
  segments 
  

   normally 
  ; 
  the 
  former 
  makes 
  amoeboid 
  movements 
  and 
  

   attempts 
  at 
  division, 
  while 
  its 
  nucleus 
  repeatedly 
  passes 
  

   through 
  the 
  initial 
  stages 
  of 
  division 
  but 
  is 
  each 
  time 
  recon- 
  

   stituted. 
  

  

  The 
  place 
  of 
  entrance 
  of 
  the 
  spermatozoon 
  often 
  varies 
  in 
  

   the 
  same 
  species 
  ; 
  this 
  can 
  naturally 
  only 
  occur 
  when 
  there 
  is 
  

   no 
  micropyle. 
  We 
  have 
  seen 
  such 
  a 
  variation 
  in 
  the 
  Axolotl 
  ; 
  

   it 
  is 
  also 
  found 
  in 
  Amphioxus 
  (Sobotta), 
  Diaptomus 
  (Ishikawa), 
  

  

  