﻿THE 
  BIONOMICS 
  OF 
  SOME 
  MALAYAN 
  ANOPHELINES. 
  141 
  

  

  Most 
  of 
  (a) 
  hatched 
  out 
  in 
  due 
  course. 
  Of 
  batch 
  (b) 
  9 
  were 
  removed 
  forthwith 
  from 
  

   •the 
  water 
  and 
  placed 
  in 
  a 
  Petri 
  dish 
  in 
  fairly 
  moist 
  filter-paper. 
  On 
  examination 
  

   48 
  hours 
  later 
  it 
  was 
  found 
  that 
  all 
  these 
  ova 
  had 
  their 
  terminal 
  caps 
  pushed 
  open 
  by 
  

   the 
  larvae, 
  which 
  could 
  be 
  seen 
  still 
  in 
  situ, 
  2 
  indeed 
  having 
  their 
  heads 
  presenting. 
  

   On 
  being 
  placed 
  in 
  water 
  all 
  hatched 
  out 
  almost 
  at 
  once, 
  2 
  sinking 
  to 
  the 
  bottom 
  

   apparently 
  in 
  an 
  exhausted 
  state, 
  and 
  struggling 
  to 
  the 
  surface, 
  after 
  a 
  few 
  seconds, 
  

   only 
  with 
  difficulty. 
  The 
  others 
  moved 
  freely, 
  though 
  with 
  their 
  bodies 
  bent 
  at 
  first 
  

   out 
  of 
  the 
  straight 
  line, 
  as 
  if 
  stiffened 
  by 
  having 
  been 
  for 
  some 
  little 
  time 
  in 
  a 
  strained 
  

   attitude. 
  Ten 
  minutes 
  after 
  removal 
  all 
  were 
  in 
  a 
  normal 
  attitude 
  in 
  the 
  water 
  and 
  

   all 
  thrived 
  subsequently. 
  

  

  Seven 
  other 
  eggs 
  from 
  batch 
  (b) 
  were 
  allowed 
  to 
  remain 
  on 
  water 
  until 
  7th 
  June 
  

   at 
  11 
  a.m., 
  having 
  been 
  afforded 
  a 
  chance 
  of 
  incubating 
  for 
  36 
  hours. 
  They 
  were 
  

   then 
  removed 
  to 
  very 
  wet 
  filter-paper 
  on 
  a 
  Petri 
  dish. 
  On 
  examination 
  24 
  hours 
  

   later 
  all 
  these 
  ova 
  were 
  observed 
  to 
  have 
  their 
  terminal 
  caps 
  widely 
  open, 
  the 
  larvae 
  

   having 
  therefore 
  probably 
  emerged 
  and 
  wriggled 
  away, 
  for 
  none 
  could 
  be 
  found. 
  

   Moisture 
  alone, 
  not 
  necessarily 
  a 
  more 
  ample 
  supply 
  of 
  water, 
  would 
  therefore 
  appear 
  

   to 
  suffice 
  for 
  the 
  hatching 
  of 
  the 
  eggs, 
  and, 
  indeed, 
  so 
  limited 
  an 
  amount 
  of 
  moisture 
  

   that 
  in 
  the 
  one 
  case 
  the 
  larvae, 
  though 
  fully 
  developed, 
  were 
  unable 
  even 
  to 
  emerge 
  

   completely. 
  The 
  balance 
  of 
  the 
  eggs 
  was 
  used 
  for 
  other 
  experimental 
  purposes. 
  

  

  The 
  evidence 
  therefore 
  suggests 
  that 
  the 
  incubation 
  of 
  Anopheline 
  eggs 
  having 
  

   once 
  reached 
  a 
  certain 
  stage 
  may 
  be 
  retarded 
  or 
  even 
  inhibited 
  by 
  adverse 
  conditions 
  ; 
  

   for 
  in 
  no 
  instance 
  did 
  hatching 
  take 
  place 
  for 
  a 
  considerable 
  number 
  of 
  hours 
  after 
  the 
  

   restoration 
  of 
  the 
  ova 
  to 
  water. 
  Such 
  a 
  provision 
  of 
  nature 
  might, 
  indeed, 
  have 
  been 
  

   expected, 
  for 
  it 
  must 
  often 
  happen 
  that 
  eggs 
  laid 
  on 
  a 
  small 
  pool 
  are 
  left 
  high 
  and 
  

   dry 
  before 
  fresh'rain 
  again 
  affords 
  the 
  stimulus 
  necessary 
  for 
  their 
  final 
  development. 
  

   It 
  is 
  hardly 
  to 
  be 
  wondered 
  at 
  that 
  freshly 
  laid 
  eggs 
  at 
  once 
  subjected 
  to 
  such 
  dis- 
  

   advantageous 
  conditions 
  uniformly 
  fail 
  to 
  develop, 
  for 
  so 
  sudden 
  a 
  removal 
  at 
  an 
  early 
  

   stage 
  from 
  a 
  moist 
  to 
  a 
  dry 
  spot 
  cannot 
  take 
  place 
  in 
  nature, 
  the 
  mere 
  fact 
  of 
  their 
  

   having 
  been 
  laid 
  -by 
  the 
  parent 
  at 
  a 
  selected 
  spot, 
  probably 
  even 
  the 
  smallest 
  pool, 
  

   having 
  ensured 
  the 
  environment 
  requisite 
  for 
  them 
  to 
  attain, 
  before 
  the 
  pool 
  has 
  

   had 
  time 
  thoroughly 
  to 
  dry 
  up, 
  a 
  degree 
  of 
  development 
  that 
  will 
  enable 
  them 
  to 
  

   retain 
  their 
  vitality. 
  But 
  as 
  has 
  now 
  also 
  been 
  shown, 
  the 
  resisting 
  powers 
  may 
  be 
  

   very 
  much 
  enhanced 
  in 
  the 
  presence 
  of 
  a 
  certain 
  amount 
  of 
  moisture, 
  and 
  development, 
  

   though 
  delayed, 
  is 
  able 
  to 
  proceed 
  as 
  surely 
  as 
  if 
  the 
  eggs 
  had 
  been 
  normally 
  laid 
  on 
  

   water. 
  It 
  would 
  appear 
  also 
  that, 
  though 
  the 
  larvae 
  are 
  fully 
  developed 
  under 
  such 
  

   circumstances 
  and 
  are 
  ready 
  to 
  hatch, 
  their 
  actual 
  emergence 
  may 
  be 
  deferred 
  without 
  

   prejudice 
  for 
  some 
  little 
  time 
  until 
  conditions 
  have 
  become 
  more 
  favourable 
  to 
  them. 
  

  

  The 
  larvae 
  of 
  A. 
  vagus 
  may 
  be 
  found 
  in 
  small, 
  drying 
  pools 
  in 
  mud, 
  in 
  situations 
  

   thoroughly 
  well 
  protected 
  both 
  from 
  sun 
  and 
  breeze, 
  and 
  where, 
  as 
  observation 
  

   has 
  shown, 
  when 
  there 
  has 
  been 
  no 
  rainfall 
  the 
  mud 
  will 
  take 
  many 
  daj^s 
  to 
  dry 
  up 
  

   completely. 
  Eggs 
  deposited 
  in 
  such 
  a 
  place 
  may 
  well 
  retain 
  their 
  vitality 
  even 
  when 
  

   there 
  is 
  insufficient 
  water 
  to 
  stimulate 
  their 
  development. 
  

  

  Investigations 
  conducted 
  for 
  the 
  purpose 
  of 
  ascertaining 
  whether 
  irregularity 
  

   in 
  hatching 
  occurs 
  as 
  a 
  normal 
  process 
  with 
  eggs 
  floating 
  on 
  water 
  have 
  shown 
  that 
  

   it 
  sometimes 
  does, 
  at 
  all 
  events 
  in 
  the 
  laboratory. 
  A 
  batch 
  of 
  ova 
  laid 
  in 
  the 
  course 
  

   of 
  a 
  night 
  by 
  a 
  female 
  Anopheline 
  may 
  all 
  hatch 
  out 
  almost 
  at 
  the 
  same 
  hour, 
  or 
  may 
  

   show, 
  under 
  -exactly 
  similar 
  circumstances, 
  differences 
  in 
  hatching 
  of 
  many 
  hours 
  

   or 
  even 
  of 
  days. 
  An 
  A. 
  fuliginosus 
  laid 
  during 
  the 
  night 
  of 
  22nd 
  to 
  23rd 
  May 
  73 
  ova. 
  

   At 
  8 
  a.m. 
  on 
  25th 
  May 
  48 
  larvae 
  had 
  emerged. 
  These 
  were 
  removed 
  ; 
  24 
  hours 
  later 
  

   14 
  more 
  larvae 
  had 
  appeared 
  ; 
  the 
  remaining 
  11 
  ova 
  failed 
  to 
  hatch. 
  An 
  A. 
  vagus 
  

   laid 
  152 
  eggs 
  during 
  the 
  night 
  30th 
  to 
  31st 
  May 
  ; 
  of 
  these 
  68 
  were 
  used 
  for 
  other 
  

   purposes, 
  and 
  84 
  were 
  kept 
  apart 
  under 
  observation. 
  The 
  majority 
  of 
  these, 
  48, 
  

   hatched 
  on 
  2nd 
  June 
  ; 
  the 
  remainder 
  were 
  left 
  just 
  as 
  they 
  were 
  until 
  4th 
  June, 
  

   when, 
  on 
  microscopic 
  examination, 
  19 
  were 
  found 
  to 
  have 
  hatched 
  ; 
  17 
  were 
  unhatched, 
  

   though 
  great 
  care 
  had 
  been 
  taken 
  that 
  at 
  no 
  time 
  were 
  any 
  of 
  these 
  eggs 
  left 
  high 
  

  

  