﻿306 
  

  

  Mr. 
  L. 
  T. 
  Hogben. 
  

  

  their 
  localisation 
  in 
  identical 
  bivalents 
  affords 
  an 
  equally 
  satisfactory 
  

   interpretation 
  of 
  the 
  phenomena 
  of 
  coupling 
  and 
  repulsion. 
  Indeed 
  were 
  

   coupling 
  and 
  repulsion 
  always 
  absolute 
  the 
  mode 
  of 
  synapsis 
  would 
  not 
  

   present 
  an 
  urgent 
  cause 
  for 
  enquiry. 
  The 
  progress 
  made 
  of 
  late 
  years, 
  

   however, 
  in 
  the 
  investigation 
  of 
  partial 
  linkages, 
  makes 
  it 
  imperative 
  for 
  

   the 
  further 
  development 
  of 
  the 
  chromosome 
  hypothesis 
  to 
  postulate 
  some 
  

   mechanism 
  for 
  the 
  exchange 
  of 
  chromatin 
  particles 
  between 
  conjugating 
  

   elements 
  ; 
  so 
  that 
  the 
  degree 
  of 
  intimacy 
  involved 
  in 
  the 
  synaptic 
  union 
  

   assumes 
  a 
  new 
  significance. 
  

  

  While 
  recognising 
  with 
  the 
  utmost 
  respect 
  the 
  brilliant 
  speculations 
  of 
  

   Prof. 
  Morgan 
  and 
  his 
  school, 
  it 
  cannot 
  be 
  truthfully 
  stated 
  that 
  there 
  exists 
  

   among 
  cytologists 
  at 
  present 
  a 
  very 
  high 
  degree 
  of 
  unanimity 
  as 
  to 
  the 
  line 
  

   along 
  which 
  the 
  solution 
  of 
  this 
  question 
  must 
  lie. 
  In 
  recent 
  years 
  the 
  

   belief 
  in 
  telosynapsis 
  (end-to-end 
  union) 
  has 
  increased 
  in 
  prestige 
  among 
  

   botanical 
  cytologists, 
  while 
  the 
  alternative 
  interpretation 
  of 
  parasynapsis 
  

   (parallel 
  conjugation) 
  has 
  found 
  greater 
  favour 
  among 
  those 
  who 
  have 
  studied 
  

   animal 
  forms. 
  In 
  attempting 
  to 
  interpret 
  satisfactorily 
  the 
  events 
  of 
  the 
  

   meiotic 
  phase 
  in 
  the 
  case 
  of 
  animals, 
  interest 
  centres 
  pre-eminently 
  in 
  

   those 
  phenomena 
  which 
  intervene 
  between 
  the 
  last 
  premeiotic 
  telophase 
  

   and 
  the 
  formation 
  of 
  the 
  " 
  bouquet 
  " 
  on 
  the 
  one 
  hand, 
  and 
  the 
  process 
  

   by 
  which 
  the 
  reduced 
  and 
  longitudinally 
  split 
  (diplotene) 
  segments 
  become 
  

   transformed 
  into 
  heterotype 
  chromosomes 
  on 
  the 
  other. 
  The 
  former 
  

   furnish 
  direct 
  evidence 
  of 
  the 
  relation 
  of 
  the 
  meiotic 
  filaments 
  to 
  the 
  

   somatic 
  chromosomes, 
  while 
  the 
  latter 
  in 
  the 
  light 
  of 
  the 
  subsequent 
  

   mitotic 
  processes 
  afford 
  indirect 
  data 
  regarding 
  the 
  mode 
  of 
  synapsis, 
  the 
  

   reality 
  of 
  synapsis 
  being 
  assumed. 
  Begarding 
  the 
  first, 
  to 
  an 
  impartial 
  

   student 
  the 
  work 
  of 
  the 
  Schreiners 
  (1) 
  1906, 
  Jannsens 
  (2) 
  1909, 
  Agar 
  (3) 
  

   1911, 
  and 
  Wilson 
  (4) 
  1912, 
  based 
  in 
  each 
  case 
  on 
  particularly 
  suitable 
  

   material 
  as 
  regards 
  both 
  size 
  and 
  seriation, 
  cannot 
  fail 
  to 
  carry 
  the 
  conviction 
  

   that 
  here 
  at 
  least 
  there 
  is 
  a 
  fusion 
  of 
  whole 
  chromosomes 
  parasyndetically 
  ; 
  

   and 
  such 
  an 
  interpretation 
  is 
  fully 
  consonant 
  with 
  the 
  usual 
  derivation 
  of 
  the 
  

   heterotype 
  chromosomes 
  by 
  separation 
  along 
  the 
  line 
  of 
  cleavage 
  in 
  the 
  

   diplotene 
  filaments. 
  There 
  are, 
  however, 
  particular 
  cases, 
  notably 
  among 
  

   Flatworms 
  and 
  Orthoptera, 
  where 
  certain 
  authors 
  (Goldschmidt(5), 
  Sutton(31), 
  

   Davis 
  (32), 
  and 
  Buchner 
  (6), 
  e.g.) 
  have 
  described 
  the 
  genesis 
  of 
  the 
  tetrads 
  

   in 
  a 
  manner 
  which 
  can 
  only 
  be 
  reconciled 
  with 
  the 
  theory 
  of 
  synapsis 
  on 
  the 
  

   assumption 
  that 
  the 
  conjugating 
  elements 
  are 
  united 
  by 
  their 
  extremities 
  

   alone. 
  In 
  the 
  case 
  of 
  plants 
  the 
  position 
  is 
  somewhat 
  different 
  ; 
  here, 
  

   according 
  to 
  the 
  most 
  recent 
  and 
  very 
  lucid 
  account 
  of 
  Miss 
  Digby 
  for 
  

   Osmunda, 
  provision 
  is 
  made 
  for 
  the 
  conjugation 
  of 
  univalents 
  in 
  the 
  second 
  

  

  