﻿448 
  J. 
  W. 
  JENKINSON. 
  

  

  Pterotracliea 
  (Boveri), 
  Cerebratulus 
  (Coe), 
  Physa 
  (von 
  

   Kostanecki). 
  

  

  The 
  tail 
  of 
  the 
  spermatozoon 
  may 
  be 
  left 
  outside 
  (Toxop- 
  

   neustes 
  [Wilson], 
  the 
  Mouse 
  [Sobotta] 
  ) 
  ; 
  but 
  in 
  the 
  great 
  

   majority 
  of 
  cases, 
  of 
  which 
  the 
  Axolotl 
  is 
  one, 
  is 
  taken 
  into 
  

   the 
  egg 
  (Polyclada 
  [Francotte 
  and 
  van 
  der 
  Stricht] 
  , 
  Amphi- 
  

   oxus 
  [van 
  der 
  Stricht], 
  Polystomum 
  [Halkin 
  and 
  Gold- 
  

   schmidt]). 
  It 
  always 
  degenerates. 
  

  

  An 
  entrance 
  funnel 
  and 
  cone 
  similar 
  to 
  those 
  observed 
  in 
  

   the 
  Axolotl 
  have 
  been 
  seen 
  in 
  Myzostoma 
  (Wheeler), 
  Ophryo- 
  

   trocha 
  (Korschelt), 
  Toxopneustes 
  (Wilson), 
  Insects 
  (Henking), 
  

   Petromyzon 
  (Bohm 
  and 
  Herfort), 
  Unio 
  (Lillie), 
  Allolobo- 
  

   phora 
  (Foot), 
  and 
  Rhynchelmis 
  (Vejdovsky). 
  

  

  The 
  most 
  accurate 
  description 
  of 
  the 
  formation 
  of 
  this 
  

   structure 
  is 
  that 
  given 
  by 
  the 
  author 
  last 
  named. 
  

  

  According 
  to 
  Vejdovsky 
  there 
  are 
  outside 
  the 
  yolk 
  two 
  

   layers, 
  an 
  external 
  alveolar 
  sheet, 
  and 
  a 
  granular 
  plasma 
  

   zone. 
  As 
  soon 
  as 
  the 
  first 
  has 
  been 
  pierced 
  by 
  the 
  head 
  of 
  

   the 
  sperm, 
  the 
  second 
  is 
  depressed 
  to 
  form 
  the 
  entrance 
  pit 
  or 
  

   funnel. 
  While 
  this 
  funnel 
  becomes 
  filled 
  by 
  a 
  granular 
  mass, 
  

   derived 
  by 
  Vejdovsky 
  from 
  the 
  ground-substance 
  of 
  the 
  cyto- 
  

   plasm, 
  the 
  alveolar 
  sheet 
  covering 
  it 
  is 
  much 
  thickened, 
  pro- 
  

   trudes 
  outwards 
  and 
  exhibits 
  a 
  radial 
  striation. 
  This 
  corre- 
  

   sponds 
  exactly 
  to 
  the 
  outer 
  dense 
  zone 
  seen 
  by 
  Fick 
  and 
  

   myself 
  in 
  the 
  Axolotl. 
  Later 
  the 
  entrance 
  cone 
  breaks 
  up 
  and 
  

   disappears. 
  

  

  A 
  very 
  similar 
  entrance 
  cone 
  is 
  described 
  by 
  Miss 
  Foot 
  in 
  

   Allolobophora, 
  and 
  by 
  Lillie 
  in 
  Unio 
  ; 
  it 
  is 
  termed 
  by 
  the 
  

   latter 
  merely 
  the 
  sperm-path. 
  

  

  Miss 
  Foot 
  and 
  Vejdovsky 
  have 
  suggested 
  that 
  the 
  acrosome 
  

   is 
  the 
  organ 
  which 
  is 
  actively 
  concerned 
  in 
  the 
  production 
  of 
  

   this 
  structure. 
  It 
  is 
  interesting 
  to 
  notice 
  that 
  according 
  to 
  

   Meves, 
  the 
  acrosome 
  of 
  the 
  Salamander 
  and 
  Guinea-pig, 
  and 
  

   according 
  to 
  von 
  Lenhossek 
  that 
  of 
  the 
  Rat, 
  arises 
  from 
  the 
  

   sphere 
  of 
  the 
  spermatid. 
  

  

  The 
  " 
  Pol-plasma 
  " 
  observed 
  by 
  both 
  Bohm 
  and 
  Herfort 
  in 
  

   Petromyzon 
  is 
  essentially 
  a 
  cone 
  of 
  entrance. 
  

  

  