﻿THE 
  BIONOMICS 
  OF 
  SOME 
  MALAYAN 
  ANOPHELINES. 
  137 
  

  

  deposited 
  on 
  the 
  fourth, 
  in 
  the 
  water 
  of 
  condensation, 
  a 
  very 
  considerable 
  mass 
  of 
  

   ova 
  in 
  which 
  incubation 
  must 
  have 
  proceeded, 
  for 
  larvae 
  hatched 
  within 
  12 
  hours 
  

   of 
  their 
  transfer 
  to 
  water. 
  An 
  A. 
  umbrosus 
  deposited 
  about 
  40 
  ova 
  in 
  a 
  dry 
  tube, 
  

   a 
  few 
  of 
  which 
  hatched 
  in 
  due 
  course, 
  having 
  been 
  placed 
  on 
  water. 
  

  

  It 
  was 
  frequently 
  found, 
  especially 
  with 
  the 
  heavy, 
  long-legged 
  Myzorhynchus 
  

   species, 
  that 
  unless 
  supports, 
  in 
  the 
  way 
  of 
  a 
  few 
  dead 
  leaves, 
  were 
  provided, 
  they 
  

   were 
  unable 
  to 
  rise 
  from 
  the 
  water, 
  and, 
  becoming 
  more 
  and 
  more 
  involved 
  in 
  the 
  

   surface 
  film, 
  eventually 
  drowned. 
  Ova 
  were 
  occasionally 
  deposited 
  on 
  such 
  leaves. 
  

   Thus 
  an 
  A 
  . 
  barbirostris 
  laid 
  58 
  ova 
  on 
  one 
  floating 
  leaf, 
  and 
  eight 
  on 
  another 
  ; 
  an 
  

   A. 
  hyrcanus 
  var. 
  paeditaeniatus 
  laid 
  a 
  batch 
  of 
  36 
  ova 
  on 
  a 
  leaf, 
  rotting 
  and 
  mildewy 
  ; 
  

   an 
  A. 
  subpictus 
  var. 
  malayensis 
  laid 
  a 
  batch 
  of 
  about 
  88 
  ova 
  on 
  another 
  leaf. 
  

  

  An 
  interesting 
  point 
  arose 
  as 
  to 
  whether 
  the 
  newly 
  hatched 
  larvae 
  in 
  such 
  cases 
  

   reached 
  the 
  water. 
  All 
  did 
  so. 
  In 
  the 
  case 
  of 
  the 
  A. 
  paeditaeniatus 
  referred 
  to, 
  the 
  

   ova 
  on 
  the 
  leaf 
  were 
  about 
  half 
  an 
  inch 
  on 
  all 
  sides 
  from 
  the 
  water 
  ; 
  and 
  the 
  young 
  

   larvae 
  were 
  found 
  in 
  the 
  water 
  on 
  all 
  sides 
  of 
  the 
  leaf. 
  

  

  It 
  was 
  impossible 
  at 
  that 
  time 
  to 
  take 
  steps 
  to 
  ascertain 
  if 
  the 
  ova 
  are 
  ever 
  so 
  

   deposited 
  in 
  nature, 
  but 
  on 
  the 
  assumption 
  that 
  this 
  may 
  be 
  the 
  case, 
  the 
  following 
  

   experiment 
  was 
  devised 
  with 
  a 
  view 
  to 
  enquiry 
  whether 
  newly 
  hatched 
  larvae 
  have 
  

   any 
  special 
  instinct 
  for 
  finding 
  their 
  way 
  to 
  water. 
  Batches 
  of 
  ova, 
  about 
  to 
  hatch, 
  

   were 
  transferred 
  to 
  a 
  strip 
  of 
  blotting 
  paper 
  on 
  a 
  glass 
  slide 
  supported 
  on 
  the 
  edge 
  

   of 
  two 
  bowls 
  of 
  water 
  so 
  that 
  the 
  ends 
  of 
  the 
  strip 
  dipped 
  into 
  the 
  water, 
  which 
  was 
  in 
  

   one 
  bowl 
  at 
  a 
  high 
  level, 
  in 
  the 
  other 
  at 
  a 
  low. 
  There 
  being 
  a 
  slow 
  current 
  from 
  the 
  

   water 
  at 
  high 
  level 
  towards 
  that 
  at 
  low 
  level, 
  it 
  was 
  thought 
  possible 
  that 
  the 
  larvae 
  

   might 
  find 
  their 
  waj' 
  against 
  stream, 
  as 
  they 
  would 
  do 
  were 
  the 
  ova 
  placed 
  in 
  nature 
  

   on 
  mud 
  at 
  the 
  edge 
  of 
  pools. 
  The 
  larvae 
  of 
  various 
  species 
  were 
  repeatedly 
  watched 
  

   wriggling 
  by 
  side 
  to 
  side 
  movements 
  in 
  both 
  directions, 
  but 
  more 
  often 
  than 
  not 
  there 
  

   were 
  fully 
  as 
  many 
  in 
  one 
  bowl 
  as 
  in 
  the 
  other. 
  

  

  Factors 
  Controlling 
  the 
  Development 
  of 
  Ova. 
  

  

  The 
  foregoing 
  observation 
  suggested 
  an 
  enquiry 
  as 
  to 
  whether, 
  as 
  has 
  been 
  shown 
  

   in 
  the 
  case 
  of 
  Aed.es 
  argent 
  ens 
  (Stcgomyia 
  fasciata) 
  , 
  the 
  development 
  of 
  Anopheline 
  ova 
  

   is 
  retarded 
  by 
  their 
  being 
  placed 
  under 
  unfavourable 
  conditions, 
  an 
  explanation 
  offered 
  

   by 
  Ross 
  to 
  account 
  for 
  Anopheline 
  periodicity 
  in 
  India, 
  though 
  this 
  is 
  less 
  likely 
  to 
  

   occur 
  in 
  a 
  climate 
  so 
  moist 
  all 
  the 
  year 
  round 
  as 
  that 
  of 
  the 
  Malay 
  States. 
  A 
  distinct 
  

   advantage 
  would 
  accrue 
  to 
  some 
  of 
  the 
  Anophelines, 
  especial!} 
  7 
  some 
  of 
  the 
  small-pool 
  

   breeders, 
  were 
  it 
  the 
  case 
  that, 
  in 
  the 
  event 
  of 
  such 
  a 
  breeding-place 
  rapidty 
  drying 
  up, 
  

   such 
  ova 
  as 
  happened 
  to 
  be 
  resting 
  on 
  the 
  surface 
  could 
  resist 
  the 
  effect 
  of 
  dessication, 
  

   and 
  could 
  maintain 
  their 
  viability 
  until 
  such 
  time 
  as 
  they 
  again 
  became 
  fortunately 
  

   circumstanced 
  for 
  hatching 
  by 
  the 
  filling 
  up 
  of 
  the 
  pool. 
  It 
  was 
  thought 
  possible 
  

   that 
  such 
  conditions, 
  often 
  accidentally 
  produced 
  in 
  the 
  laboratory 
  by 
  the 
  gradual 
  

   lowering 
  by 
  evaporation 
  of 
  the 
  water 
  level 
  in 
  basins 
  containing 
  ova, 
  as 
  a 
  result 
  of 
  

   which 
  the 
  ova, 
  which 
  often 
  collect 
  through 
  capillarv 
  attraction 
  at 
  the 
  sides, 
  become 
  

   high 
  and 
  dry, 
  might 
  account 
  for 
  the 
  marked 
  inequality 
  of 
  size 
  of 
  larvae 
  compiling 
  

   one 
  family 
  ; 
  such 
  ova 
  hatching 
  only 
  when 
  it 
  became 
  necessary 
  to 
  add 
  a 
  fresh 
  supply 
  

   of 
  water. 
  In 
  a 
  series 
  of 
  experiments 
  the 
  ova 
  removed 
  from 
  the 
  water 
  at 
  various 
  stages 
  

   of 
  incubation 
  were 
  allowed 
  to 
  dry 
  in 
  the 
  laboratory 
  at 
  ordinary 
  temperature, 
  and 
  were 
  

   restored 
  to 
  water 
  at 
  varying 
  intervals, 
  the 
  results 
  being 
  noted. 
  The 
  following 
  are 
  

   typical 
  of 
  the 
  many 
  experiments 
  so 
  conducted 
  : 
  — 
  

  

  Of 
  36 
  ova 
  laid 
  by 
  an 
  A. 
  vagus 
  during 
  the 
  night 
  of 
  18th 
  to 
  19th 
  May 
  all 
  were 
  

   removed 
  from 
  the 
  water 
  at 
  8 
  a.m. 
  on 
  19th, 
  being 
  then 
  approximately 
  under 
  seven 
  

   hours 
  old. 
  They 
  were 
  divided 
  into 
  two 
  batches, 
  (a) 
  of 
  20, 
  and 
  (b) 
  of 
  16, 
  which 
  were 
  

   gradually 
  dried 
  on 
  blotting 
  paper 
  in 
  the 
  laboratory. 
  Twenty-four 
  hours 
  later 
  batch 
  

   (a) 
  was 
  restored 
  to 
  water, 
  and 
  at 
  the 
  end 
  of 
  a 
  further 
  period 
  of 
  24 
  hours 
  batch 
  (b) 
  

   also 
  was 
  restored. 
  No 
  hatching 
  had 
  taken 
  place 
  at 
  the 
  end 
  of 
  three 
  days 
  more, 
  

  

  