﻿356 
  

  

  F. 
  W. 
  FISKE. 
  

  

  These 
  data 
  indicate 
  that 
  whereas 
  the 
  density 
  of 
  male 
  flies 
  had 
  been 
  reduced 
  from 
  

   30 
  '0 
  caught 
  per 
  boy 
  per 
  hour 
  on 
  the 
  6th 
  to 
  151 
  on 
  the 
  8th, 
  that 
  of 
  female 
  flies 
  had 
  

   not 
  been 
  appreciably 
  reduced 
  — 
  exactly 
  as 
  though 
  the 
  females 
  were 
  actually 
  present 
  

   on 
  the 
  island 
  but 
  for 
  some 
  reason 
  not 
  so 
  easily 
  caught 
  as 
  either 
  (a) 
  the 
  males 
  on 
  the 
  

   same 
  island, 
  or 
  (6) 
  the 
  females 
  on 
  Bulago 
  Island 
  (Table 
  I). 
  

  

  This 
  hypothetical 
  explanation 
  for 
  a 
  low 
  percentage 
  of 
  females 
  in 
  the 
  catch 
  suggested 
  

   the 
  experiment 
  of 
  catching 
  all 
  the 
  flies 
  from 
  an 
  islet. 
  Tavu 
  was 
  rather 
  larger 
  than 
  

   convenient 
  and 
  the 
  yet 
  smaller 
  islet 
  of 
  Lula 
  (Fig. 
  I) 
  with 
  an 
  area 
  of 
  hardly 
  more 
  

   than 
  10,000 
  square 
  yards 
  was 
  selected. 
  

  

  The 
  results 
  of 
  this 
  experiment 
  are 
  presented 
  in 
  Table 
  VI. 
  It 
  was 
  not 
  carried 
  

   to 
  a 
  final 
  conclusion 
  because 
  of 
  the 
  time 
  which 
  would 
  be 
  required 
  to 
  catch 
  all 
  the 
  

   flies 
  emerging 
  from 
  pupae 
  on 
  the 
  island 
  (at 
  least 
  three 
  weeks 
  longer 
  than 
  the 
  period 
  

   devoted 
  to 
  it), 
  but 
  it 
  was 
  carried 
  far 
  enough 
  to 
  demonstrate 
  conclusively 
  that 
  a 
  very 
  

   low 
  percentage 
  of 
  females 
  may 
  be 
  due 
  to 
  the 
  relative 
  inactivity, 
  and 
  not, 
  as 
  had 
  

   always 
  been 
  assumed, 
  to 
  the 
  absence 
  of 
  the 
  sex. 
  

  

  I 
  (o). 
  The 
  Percentage 
  of 
  Females 
  among 
  caught 
  Flies 
  as 
  an 
  Index 
  to 
  Food 
  Supply. 
  

  

  An 
  analysis 
  of 
  the 
  data 
  presented 
  (in 
  part) 
  in 
  Table 
  VI 
  and 
  secured 
  during 
  the 
  

   course 
  of 
  the 
  Lula 
  experiment 
  above 
  described 
  d'sclosed 
  the 
  curious 
  fact 
  that 
  although 
  

   the 
  catch 
  of 
  males 
  fell 
  sharply 
  from 
  14 
  '0 
  per 
  boy 
  per 
  hour 
  on 
  the 
  the 
  first 
  day 
  to 
  

   2*6 
  and 
  1*7 
  on 
  the 
  morning 
  and 
  afternoon 
  of 
  the 
  third 
  day 
  (see 
  Table 
  VII) 
  ; 
  that 
  of 
  

   females 
  rose 
  strikingly 
  from 
  "9 
  per 
  boy 
  per 
  hour 
  on 
  the 
  first 
  to 
  4 
  '5 
  and 
  4*4 
  on 
  the 
  

   morning 
  and 
  afternoon 
  of 
  the 
  third 
  day. 
  Otherwise 
  stated, 
  the 
  density 
  of 
  active 
  

   male 
  flies 
  was 
  quickly 
  and 
  permanently 
  reduced 
  to 
  one- 
  eighth 
  or 
  less 
  of 
  the 
  original, 
  

   but 
  that 
  of 
  active 
  female 
  flies 
  actually 
  increased 
  by 
  no 
  less 
  than 
  five 
  times 
  during 
  

   the 
  same 
  period 
  that 
  that 
  of 
  the 
  males 
  was 
  being 
  reduced 
  by 
  seven- 
  eighths. 
  

  

  

  

  

  Table 
  VII. 
  

  

  

  

  Analysis 
  of 
  Catch 
  of 
  Fly 
  made 
  on 
  Lula 
  Islet 
  showing 
  Variation 
  in 
  

  

  Activity 
  of 
  

  

  

  Females. 
  

  

  

  

  

  Density* 
  of 
  Active 
  

  

  Flies. 
  

  

  Period 
  

  

  

  

  

  (November 
  1913). 
  

  

  

  

  

  

  

  Males. 
  

  

  Females. 
  

  

  Total. 
  

  

  18th 
  Afternoon 
  . 
  

  

  

  14-0 
  

  

  •9 
  

  

  14-9 
  

  

  19th 
  Morning 
  . 
  

  

  

  

  

  9-7 
  

  

  2*2 
  

  

  11-9 
  

  

  19th 
  Afternoon 
  

  

  

  . 
  

  

  

  3*5 
  

  

  2-8 
  

  

  6-3 
  

  

  20th 
  Morning 
  . 
  

  

  

  

  

  2-6 
  

  

  4-5 
  

  

  7*1 
  

  

  20th 
  Afternoon 
  

  

  

  

  

  1-7 
  

  

  4-4 
  

  

  6-1 
  

  

  21st 
  All 
  Day 
  . 
  

  

  

  . 
  

  

  

  1-8 
  

  

  4 
  1 
  

  

  5-9 
  

  

  22nd 
  

  

  

  

  

  1-0 
  

  

  1-6 
  

  

  2-6 
  

  

  24th 
  

  

  

  

  

  •7 
  

  

  1-7 
  

  

  2-4 
  

  

  25th 
  

  

  

  . 
  

  

  

  •9 
  

  

  2-9 
  

  

  3-8 
  

  

  26th 
  

  

  

  

  

  •7 
  

  

  1-4 
  

  

  2-1 
  

  

  27th 
  Morning 
  . 
  

  

  

  . 
  

  

  

  •6 
  

  

  1-6 
  

  

  2-2 
  

  

  : 
  By 
  " 
  density 
  " 
  is 
  meant 
  the 
  number 
  of 
  flies 
  which 
  can 
  be 
  caught 
  per 
  boy 
  per 
  hour. 
  

  

  