﻿Studies 
  on 
  Synapsis. 
  

  

  279 
  

  

  nine 
  chromosomes, 
  which 
  number 
  is 
  doubled 
  prior 
  to 
  the 
  first 
  segmentation 
  

   division. 
  

  

  Significance 
  of 
  the 
  Polar 
  Divisions. 
  

  

  The 
  character 
  of 
  the 
  chromosome 
  cycle 
  in 
  the 
  production 
  of 
  drones 
  in 
  the 
  

   Hymenoptera 
  may 
  now 
  be 
  regarded 
  as 
  settled. 
  In 
  those 
  completely 
  partho- 
  

   genetic 
  species 
  which 
  produce 
  thelytokous 
  ova 
  without 
  impregnation 
  our 
  

   knowledge 
  is 
  scanty, 
  but 
  it 
  seems 
  clear 
  that 
  the 
  same 
  uniformity 
  does 
  not 
  

   prevail 
  ; 
  the 
  only 
  really 
  satisfactory 
  account 
  is 
  that 
  of 
  Doncaster 
  who 
  

   investigated 
  the 
  agamic 
  generation 
  of 
  Neuroterus, 
  in 
  which 
  form 
  there 
  are 
  no 
  

   polar 
  bodies 
  extruded 
  by 
  those 
  eggs 
  which 
  develop 
  into 
  females. 
  This 
  is 
  not, 
  

   however, 
  typical 
  of 
  the 
  Hymenoptera 
  where 
  in 
  several 
  cases 
  agamic 
  female- 
  

   producing 
  eggs 
  are 
  known 
  to 
  form 
  two 
  polar 
  bodies, 
  as 
  in 
  the 
  case 
  of 
  

   Rhodites, 
  Pcecilosoma 
  and 
  Croesus. 
  These 
  forms 
  also 
  contrast 
  with 
  the 
  

   cytological 
  behaviour 
  of 
  female-producing 
  eggs 
  among 
  parthenogenetic 
  

   organisms 
  belonging 
  to 
  other 
  groups, 
  where 
  as 
  a 
  rule 
  females 
  are 
  produced 
  

   from 
  eggs 
  which 
  extrude 
  only 
  one 
  polar 
  body 
  by 
  an 
  equational 
  division. 
  

  

  The 
  question 
  now 
  arises 
  ; 
  what 
  relation 
  have 
  the 
  chromosomes 
  that 
  

   separate 
  during 
  the 
  interkinesis 
  preceding 
  segmentation 
  to 
  one 
  another 
  ? 
  

   There 
  seem 
  to 
  be 
  two 
  possible 
  ways 
  of 
  interpreting 
  Henking's 
  " 
  Verdoppelung": 
  

   (1) 
  the 
  polar 
  mitoses 
  are 
  both 
  equational, 
  and 
  the 
  doubling 
  of 
  the 
  chromo- 
  

   somes 
  in 
  the 
  female 
  pronucleus 
  is 
  a 
  disjunction 
  of 
  bivalents 
  ; 
  or 
  (2) 
  the 
  

   chromosomes 
  which 
  pair 
  in 
  synapsis 
  are 
  equivalent 
  daughter 
  halves 
  of 
  a 
  

   single 
  chromosome 
  which 
  has 
  divided 
  before 
  segmentation 
  begins.* 
  Apart 
  

   from 
  the 
  question 
  of 
  sex 
  determination, 
  either 
  hypothesis 
  is 
  equally 
  accept- 
  

   able, 
  an 
  objection, 
  however, 
  to 
  the 
  first 
  being 
  the 
  extraordinary 
  similarity 
  

   of 
  the 
  separation 
  of 
  polar 
  nuclei 
  in 
  female-producing 
  eggs 
  of 
  Rhodites 
  and 
  

   male-producing 
  eggs 
  of 
  Neuroterus, 
  which 
  are 
  probably 
  reduced 
  qualitatively 
  

   and 
  quantitatively. 
  The 
  second 
  hypothesis 
  in 
  the 
  case 
  of 
  Rhodites 
  offers 
  no 
  

   explanation 
  of 
  the 
  occasional 
  appearance 
  of 
  males, 
  and 
  does 
  not 
  fall 
  into 
  

   line 
  with 
  conclusions 
  regarding 
  sex-determination 
  based 
  upon 
  the 
  study 
  of 
  

   other 
  Hymenoptera. 
  Nachtsheim, 
  to 
  account 
  for 
  the 
  difference 
  of 
  sex 
  in 
  

   fertilised 
  and 
  unfertilised 
  eggs 
  of 
  the 
  bee, 
  has 
  put 
  forward 
  the 
  theory 
  that, 
  of 
  

   the 
  32 
  chromosomes 
  in 
  the 
  oogonial 
  mitoses 
  of 
  Apis, 
  30 
  are 
  somatic 
  and 
  two 
  

   are 
  X-chromosomes 
  ; 
  at 
  maturation 
  reductiou 
  occurs, 
  so 
  that 
  the 
  female 
  

   pronucleus 
  should 
  have 
  the 
  constitution 
  15-X, 
  thus 
  a 
  virgin 
  egg 
  would 
  have 
  

   a 
  single 
  sex 
  chromosome, 
  while 
  a 
  fertilised 
  egg 
  will 
  have 
  two. 
  The 
  sexual 
  

   differentiation 
  in 
  the 
  chromosome 
  cycle 
  of 
  Apis 
  is 
  by 
  this 
  means 
  made 
  to 
  

   agree 
  with 
  the 
  case 
  of 
  those 
  insects 
  in 
  which 
  maleness 
  is 
  associated 
  with 
  a 
  

  

  * 
  Nachtsheim's 
  work 
  on 
  the 
  segmentation 
  of 
  the 
  drone 
  eggs 
  of 
  the 
  bee 
  renders 
  such 
  

   a 
  hypothesis 
  not 
  improbable 
  a 
  priori. 
  

  

  