﻿MATDKATION, 
  ETC 
  , 
  OF 
  THIil 
  EGG 
  OP 
  THE 
  AXOLOTL. 
  443 
  

  

  In 
  Invertebrates 
  it 
  is 
  the 
  very 
  general 
  rule 
  for 
  the 
  asters 
  

   and 
  centrosomes 
  of 
  the 
  pohxr 
  spindles 
  to 
  be 
  well 
  developed 
  

   (Platyhelmia 
  [Francotte, 
  van 
  der 
  Stricht 
  (1898), 
  von 
  

   Klinckowstrom, 
  Gardiner, 
  Hennegny, 
  Goldschmidt, 
  Halkin], 
  

   Nemertines 
  [Coe, 
  von 
  Kostanecki 
  (1902)], 
  Mollusca 
  [Lillie, 
  

   von 
  Kostanecki 
  (1896), 
  Boveri 
  (1890), 
  Mark, 
  Linville, 
  Griffin, 
  

   Garnanlt], 
  Ch^topoda 
  [Foot, 
  Vejdovsky, 
  Korschelt, 
  Griffin], 
  

   Arthropoda 
  [Ishikawa], 
  Echinoderms 
  [Matthews], 
  Ascidia 
  

   [Castle]) 
  ; 
  but 
  centrosomes 
  are 
  stated 
  to 
  be 
  absent 
  in 
  Ascaris 
  

   by 
  Boveri 
  (1887), 
  though 
  this 
  is 
  denied 
  by 
  Cftrnoy 
  and 
  

   others 
  ; 
  in 
  Sagitta 
  by 
  the 
  same 
  observer 
  (1890), 
  and 
  by 
  

   Brauer 
  (1892) 
  in 
  Branchipus. 
  

  

  Considering 
  the 
  wide-spread 
  occurrence 
  of 
  the 
  centrosorae 
  

   as 
  an 
  active 
  cell-organ 
  I 
  believe 
  that 
  the 
  ill-defined 
  body 
  

   which 
  is 
  undoubtedly 
  present 
  in 
  these 
  cases 
  at 
  the 
  spindle 
  

   pole 
  may 
  be 
  looked 
  on 
  as 
  a 
  physiological 
  centre, 
  even 
  though 
  

   it 
  contains 
  no 
  corpuscle 
  which 
  will 
  react 
  to 
  the 
  iron-hfema- 
  

   toxylin 
  stain; 
  and 
  considering 
  what 
  we 
  now 
  know 
  of 
  the 
  

   growth 
  and 
  metamorphosis 
  of 
  the 
  centrosome 
  it 
  ought 
  not 
  to 
  

   surprise 
  us 
  that 
  this 
  body 
  should 
  in 
  certain 
  cases 
  not 
  merely 
  

   cast 
  off 
  the 
  peripheral 
  portion 
  of 
  its 
  substance, 
  as 
  it 
  admit- 
  

   tedly 
  does, 
  but 
  wholly 
  disappear 
  into 
  the 
  aster 
  to 
  which 
  it 
  

   gives 
  rise. 
  I 
  shall 
  have 
  to 
  recur 
  to 
  this 
  point 
  later 
  on. 
  

  

  Many 
  authors 
  besides 
  Carnoy 
  have 
  attributed 
  to 
  the 
  first 
  

   polar 
  spindle 
  an 
  intra-nuclear 
  origin, 
  either 
  in 
  whole 
  or 
  in 
  

   part. 
  

  

  In 
  Ascaris 
  (Boveri 
  [1887]), 
  in 
  Branchipus 
  (Brauer 
  [1892]), 
  

   and 
  in 
  Opliryotrocha 
  (Korschelt) 
  the 
  germinal 
  vesicle 
  becomes 
  

   dii-ectly 
  ti^ansformed 
  into 
  the 
  spindle. 
  

  

  In 
  other 
  cases 
  the 
  nuclear 
  membrane 
  disappears 
  under 
  the 
  

   influence 
  of 
  the 
  astral 
  rays, 
  and 
  the 
  equatorial 
  portion 
  of 
  the 
  

   spindle 
  arises 
  in 
  the 
  interior 
  of 
  the 
  nucleus 
  (Polyclada 
  

   [Francotte 
  and 
  van 
  der 
  Stricht 
  (1898)], 
  Cerebratulus 
  [Coe] 
  

   and 
  others). 
  Such 
  a 
  double— 
  extra- 
  and 
  intra-nuclear 
  — 
  

   origin 
  of 
  the 
  fibres 
  also 
  occurs 
  in 
  the 
  fertilisation 
  spindle. 
  I 
  

   have 
  described 
  this 
  above 
  for 
  the 
  Axolotl 
  ; 
  it 
  has 
  also 
  been 
  

   observed 
  in 
  Polyclada, 
  Cerebratulus, 
  Thalassema, 
  Ophryo- 
  

  

  