﻿INVESTIGATIONS 
  INTO 
  THE 
  BIONOMICS 
  OF 
  GLOSSINA 
  PALPALIS. 
  369 
  

  

  This 
  same 
  phenomenon 
  was 
  observed 
  a 
  second 
  time 
  under 
  different 
  conditions 
  

   in 
  a 
  catch 
  made 
  on 
  the 
  23rd 
  September 
  1914 
  at 
  a 
  point 
  on 
  the 
  island 
  of 
  Bussi, 
  

   where 
  two 
  boys 
  worked 
  ankle-deep 
  in 
  water 
  outside 
  a 
  thick 
  mass 
  of 
  reedy 
  vegetation 
  

   that 
  prohibited 
  landing, 
  and 
  two 
  other 
  boys 
  on 
  a 
  point 
  of 
  shelving 
  rock, 
  backed 
  

   by 
  an 
  open 
  space 
  and 
  bushy 
  forest 
  of 
  a 
  type 
  much 
  favoured 
  by 
  fly 
  as 
  shelter. 
  The 
  

   poorly 
  sheltered, 
  reed-fringed 
  point 
  on 
  the 
  shore 
  was 
  only 
  about 
  100 
  yards 
  distant 
  

   from 
  the 
  attractively 
  sheltered 
  point. 
  

  

  The 
  catch 
  was 
  as 
  follows, 
  for 
  the 
  four 
  boys 
  for 
  half 
  an 
  hour 
  : 
  

  

  Well 
  sheltered 
  Poorly 
  sheltered 
  

   Point. 
  Point. 
  

  

  Catch 
  per 
  boy 
  hour 
  — 
  

  

  Males 
  49-0 
  8*0 
  

  

  Females 
  3*0 
  13 
  '0 
  

  

  Female 
  percentage 
  . 
  . 
  . 
  . 
  . 
  . 
  5 
  '8 
  60*8 
  

  

  As 
  before, 
  there 
  is 
  an 
  extraordinary 
  discrepancy 
  in 
  sex 
  ratio 
  between 
  points 
  

   separated, 
  in 
  this 
  case, 
  by 
  only 
  about 
  100 
  yards. 
  And 
  in 
  both 
  cases 
  the 
  high 
  

   percentage 
  of 
  females 
  is 
  associated 
  with 
  a 
  type 
  of 
  vegetation 
  known 
  to 
  be 
  especially 
  

   repugnant 
  as 
  shelter 
  and 
  the 
  low 
  percentage 
  with 
  a 
  type 
  of 
  vegetation 
  known 
  

   to 
  be 
  attractive. 
  

  

  A 
  hypothetical 
  explanation 
  for 
  this 
  phenomenon, 
  which 
  has 
  withstood 
  all 
  tests 
  

   applied 
  to 
  it, 
  is 
  as 
  follows 
  : 
  — 
  

  

  (a) 
  The 
  body 
  or 
  mass 
  of 
  active 
  flies 
  is 
  continually 
  in 
  movement, 
  and 
  

   streams 
  of 
  flies 
  are 
  continually 
  passing 
  points 
  along 
  shore 
  (see 
  Sect. 
  Ill 
  (a) 
  ). 
  

  

  (b) 
  These 
  streams 
  of 
  moving 
  flies 
  are 
  made 
  up 
  of 
  (1) 
  food- 
  hunting 
  flies 
  

   of 
  both 
  sexes, 
  which 
  compose 
  a 
  variable 
  proportion 
  dependent 
  upon 
  abundance 
  

   of 
  food 
  and 
  which 
  move 
  rapidly 
  ; 
  and 
  (2) 
  male 
  flies 
  which 
  are 
  not 
  seeking 
  

   food, 
  but 
  which 
  frequent 
  the 
  routes 
  followed 
  by 
  food-hunting 
  flies, 
  and 
  which 
  

   move 
  much 
  more 
  slowly 
  (see 
  Sect. 
  Ill 
  (h) 
  ). 
  

  

  (c) 
  The 
  relatively 
  idle 
  and 
  lingering 
  males 
  tend 
  to 
  prolong 
  their 
  sojourns 
  

   at 
  points 
  where 
  sheltering 
  vegetation 
  is 
  of 
  the 
  most 
  attractive 
  type, 
  and 
  to. 
  

   pass 
  quickly, 
  or 
  not 
  at 
  all, 
  by 
  points 
  where 
  the 
  vegetation 
  is 
  of 
  an 
  unattractive 
  

   type. 
  It 
  follows 
  that 
  (1) 
  density 
  of 
  active 
  males 
  will 
  be 
  greatest 
  where 
  shelter 
  

   is 
  most 
  attractive, 
  and 
  least 
  where 
  it 
  is 
  least 
  attractive, 
  and 
  (2) 
  that 
  the 
  

   percentage 
  of 
  females 
  amongst 
  caught 
  flies 
  will 
  be 
  greatest 
  where 
  shelter 
  is 
  

   least, 
  and 
  least 
  where 
  shelter 
  is 
  most 
  attractive 
  to 
  the 
  lingering 
  males 
  

   (because 
  food-hunting 
  flies 
  must, 
  for 
  several 
  reasons,* 
  consist 
  principally 
  

   of 
  females). 
  

  

  When 
  confirmation 
  of 
  this 
  hypothesis 
  was 
  sought 
  it 
  was 
  found 
  on 
  every 
  hand, 
  

   not 
  only 
  in 
  new 
  catching 
  experiments 
  and 
  fly 
  survey 
  work, 
  but 
  in 
  old 
  records, 
  made 
  

  

  * 
  These 
  reasons 
  include 
  the 
  following 
  : 
  — 
  

  

  1st. 
  Because 
  the 
  females 
  in 
  any 
  district 
  or 
  region 
  appear 
  to 
  outnumber 
  the 
  males 
  

   (see 
  Sect. 
  I 
  (d) 
  ). 
  

  

  2nd. 
  Becaus 
  , 
  the 
  females 
  must 
  nourish 
  their 
  young 
  as 
  well 
  as 
  themselves, 
  and 
  most 
  

   probably 
  require 
  food 
  somewhat 
  more 
  frequently, 
  in 
  nature, 
  than 
  males. 
  

  

  3rd. 
  Because 
  the 
  males 
  are 
  normally 
  active 
  at 
  all 
  times 
  during 
  good 
  weather, 
  and 
  

   are 
  more 
  apt 
  than 
  the 
  females 
  to 
  encounter 
  host 
  animals 
  without 
  specifically 
  seeking 
  

   for 
  them. 
  

  

  