﻿18 
  

  

  W. 
  A. 
  LAMBORX. 
  

  

  clearing 
  only 
  on 
  the 
  distribution 
  of 
  A. 
  umbrosus, 
  as 
  a 
  necessary 
  preliminary 
  to 
  

   making 
  a 
  study 
  of 
  the 
  ultimate 
  factors 
  concerned 
  in 
  its 
  disappearance, 
  the 
  writer 
  

   caused 
  the 
  bush 
  surrounding 
  the 
  pool 
  to 
  be 
  partly 
  cleared, 
  and 
  then, 
  three 
  months 
  

   later, 
  to 
  be 
  completely 
  cut 
  down. 
  Collections 
  were 
  made 
  at 
  intervals 
  both 
  before 
  

   and 
  after 
  clearing, 
  and 
  the 
  results 
  are 
  given 
  in 
  the 
  following 
  table 
  : 
  — 
  

  

  TABLE 
  V. 
  

  

  Date. 
  

  

  A. 
  umbrosus. 
  

  

  A 
  . 
  barbirostris. 
  

  

  A. 
  hyrcanus. 
  

  

  A 
  . 
  aconitus. 
  

  

  20.vii.20 
  

  

  113 
  

  

  

  

  

  23.vii.20 
  

  

  32 
  

  

  — 
  

  

  — 
  

  

  — 
  . 
  

  

  12.viii.20 
  

  

  130 
  

  

  — 
  

  

  — 
  

  

  — 
  

  

  24.viii.20 
  

  

  184 
  

  

  — 
  

  

  — 
  

  

  — 
  

  

  2.ix.20 
  

  

  193 
  

  

  — 
  

  

  — 
  

  

  — 
  

  

  6.ix.20 
  

  

  130 
  

  

  — 
  

  

  — 
  

  

  — 
  

  

  22.ix.20 
  (here 
  bush 
  partly 
  

  

  

  

  

  

  cleared) 
  

  

  11 
  

  

  — 
  

  

  — 
  

  

  — 
  

  

  lO.x.20 
  

  

  66 
  

  

  — 
  

  

  — 
  

  

  — 
  

  

  4.xi.20 
  

  

  2 
  

  

  2 
  

  

  3 
  

  

  — 
  

  

  8.xii.20 
  

  

  10 
  

  

  — 
  

  

  14 
  

  

  — 
  

  

  30.xii.20 
  (here 
  bush 
  completely 
  

  

  

  

  

  

  cleared) 
  

  

  114 
  

  

  365 
  

  

  110 
  

  

  — 
  

  

  17.1.21 
  

  

  48 
  

  

  70 
  

  

  — 
  

  

  — 
  

  

  27.L21 
  

  

  — 
  

  

  140 
  

  

  — 
  

  

  — 
  

  

  19.ii.21 
  

  

  — 
  

  

  76 
  

  

  50 
  

  

  — 
  

  

  25.ii.21 
  

  

  — 
  

  

  — 
  

  

  — 
  

  

  — 
  

  

  5.iii.21 
  

  

  — 
  

  

  28 
  

  

  — 
  

  

  — 
  

  

  ll.iii.21 
  

  

  — 
  

  

  37 
  

  

  3 
  

  

  — 
  

  

  6.iv.21 
  

  

  ~" 
  

  

  24 
  

  

  2 
  

  

  1 
  

  

  Some 
  diminution 
  of 
  A 
  . 
  umbrosus 
  therefore 
  resulted 
  from 
  the 
  partial 
  clearing 
  ; 
  

   the 
  invasion 
  by 
  A. 
  hyrcanus 
  and 
  A. 
  barbirostris, 
  which 
  took 
  place 
  at 
  the 
  same 
  time, 
  

   was 
  in 
  accordance 
  with 
  expectation. 
  The 
  final 
  disappearance 
  of 
  A. 
  umbrosus 
  and 
  

   its 
  replacement 
  by 
  the 
  two 
  other 
  species 
  when 
  the 
  clearing 
  had 
  been 
  completed 
  are 
  

   well 
  brought 
  out 
  by 
  the 
  figures. 
  What 
  can 
  be 
  the 
  causes 
  at 
  work 
  ? 
  

  

  One 
  might 
  be 
  disposed 
  to 
  attribute 
  the 
  failure 
  of 
  the 
  former 
  species 
  merely 
  to 
  

   the 
  letting 
  in 
  of 
  sunlight 
  ; 
  producing, 
  perhaps 
  by 
  direct 
  action, 
  or 
  by 
  affecting 
  the 
  

   gas 
  content 
  of 
  the 
  water, 
  a 
  change 
  of 
  the 
  algal 
  flora. 
  It 
  was 
  not 
  possible 
  to 
  decide 
  

   that 
  these 
  larvae 
  died 
  as 
  the 
  direct 
  result 
  of 
  exposure 
  to 
  the 
  sun, 
  on 
  account 
  of 
  the 
  

   difficulty, 
  which 
  was 
  not 
  overcome 
  until 
  just 
  before 
  the 
  work 
  was 
  terminated 
  by 
  

   leave, 
  of 
  keeping 
  the 
  larvae 
  long 
  alive 
  in 
  captivity 
  and 
  getting 
  them 
  to 
  grow. 
  The 
  

   disappearance 
  would 
  hardly 
  have 
  been 
  due 
  to 
  the 
  fouling 
  of 
  the 
  water 
  by 
  the 
  vegetable 
  

   matter 
  which 
  fell 
  in 
  during 
  clearing, 
  since 
  the 
  pool 
  always 
  received 
  its 
  share 
  of 
  the 
  

   carpet 
  of 
  leaves 
  elsewhere. 
  

  

  Whatever 
  the 
  causes 
  which 
  lead 
  to 
  so 
  profound 
  an 
  alteration 
  of 
  the 
  Anopheline 
  

   fauna, 
  they 
  must 
  be 
  apparently 
  trivial 
  ones. 
  Unfortunately 
  no 
  water 
  was 
  collected 
  

   for 
  analysis 
  before 
  clearing 
  was 
  effected, 
  but 
  in 
  the 
  following 
  table 
  is 
  given 
  the 
  result 
  

   of 
  an 
  anatysis 
  by 
  Mr. 
  Blair 
  of 
  the 
  water 
  subsequent 
  to 
  clearing 
  and 
  of 
  water 
  from 
  

   another 
  pool 
  in 
  secondary 
  bush 
  elsewhere, 
  which 
  afforded 
  the 
  larvae 
  of 
  A. 
  umbrosus 
  

   in 
  pure 
  culture. 
  

  

  