﻿374 
  W. 
  F. 
  FISKE. 
  

  

  the 
  unattractive 
  character 
  of 
  the 
  environment* 
  at 
  these 
  points 
  retarding 
  the 
  movement 
  

   of 
  the 
  relatively 
  idle 
  and 
  inactive 
  males 
  along 
  shore. 
  These 
  males 
  were 
  concentrated 
  

   along 
  the 
  short 
  reach 
  of 
  shore 
  including 
  points 
  45 
  and 
  46 
  ; 
  and 
  elsewhere 
  it 
  was 
  almost 
  

   entirely 
  the 
  actively 
  moving, 
  food-hunting 
  flies 
  that 
  were 
  caught. 
  

  

  This 
  particular 
  colony 
  of 
  Mujuzi 
  is 
  in 
  several 
  other 
  respects 
  one 
  of 
  the 
  most 
  interest- 
  

   ing 
  and 
  deserving 
  of 
  study 
  of 
  any 
  encountered 
  on 
  either 
  island 
  or 
  mainland. 
  It 
  

   is 
  mentioned 
  elsewhere, 
  and 
  a 
  graph 
  of 
  it 
  is 
  presented 
  facing 
  p. 
  388. 
  It 
  was 
  non- 
  

   existent 
  in 
  1906 
  but 
  came 
  into 
  being 
  subsequently 
  as 
  a 
  result 
  of 
  environmental 
  

   changes 
  described 
  on 
  p. 
  458. 
  

  

  Ill 
  (/). 
  The 
  Full 
  Significance 
  of 
  the 
  Phenomenon 
  of 
  Sex 
  Disparity 
  in 
  

   Glossina 
  palpalis 
  with 
  Relation 
  to 
  Food 
  Supply, 
  Shelter 
  and 
  Movements 
  

   of 
  Fly. 
  

  

  The 
  phenomenon 
  of 
  a 
  variable 
  ratio 
  between 
  the 
  sexes 
  of 
  active 
  flies 
  of 
  Glossina 
  

   palpalis 
  proved 
  on 
  investigation, 
  as 
  I 
  have 
  attempted 
  to 
  make 
  clear, 
  to 
  be 
  replete 
  

   with 
  interest 
  and 
  significance. 
  

  

  Taken 
  over 
  any 
  considerable 
  district 
  or 
  region 
  it 
  is 
  a 
  fair 
  index 
  to 
  the 
  abundance 
  

   of 
  preferred 
  hosts, 
  and 
  thereby 
  of 
  the 
  relative 
  immunity 
  of 
  man 
  to 
  attack 
  (see 
  

   Sects. 
  I 
  and 
  II). 
  

  

  Taken 
  locally, 
  point 
  by 
  point 
  along 
  a 
  reach 
  of 
  shore, 
  and 
  coupled 
  with 
  the 
  local 
  

   density 
  of 
  active 
  males 
  at 
  these 
  same 
  points, 
  it 
  becomes 
  a 
  subtle 
  index 
  to 
  the 
  

   attractiveness 
  or 
  repulsiveness 
  of 
  the 
  local 
  environment 
  to 
  fly. 
  This 
  fact 
  having 
  

   been 
  conclusively 
  proved, 
  thereafter 
  data 
  in 
  such 
  local 
  variations 
  become 
  of 
  really 
  

   great 
  value 
  in 
  reaching 
  conclusions 
  concerning 
  the 
  relative 
  attraction 
  of 
  various 
  

   types 
  of 
  vegetation, 
  etc., 
  to 
  the 
  flies. 
  

  

  Finally, 
  through 
  study 
  of 
  this 
  sex 
  disparity 
  and 
  its 
  causes, 
  a 
  very 
  clear 
  conception 
  

   is 
  obtained 
  of 
  the 
  ordinary 
  movements 
  of 
  the 
  flies 
  along 
  the 
  shores 
  of 
  the 
  lake, 
  banks 
  

   of 
  stream, 
  borders 
  of 
  woodland, 
  game 
  trails, 
  foot-paths, 
  or 
  other 
  favourite 
  courses. 
  

   A 
  great 
  many 
  little 
  experiments 
  and 
  informal 
  observations 
  were 
  made 
  to 
  ascertain 
  

   the 
  routes 
  most 
  freely 
  followed 
  by 
  the 
  active 
  food-hunting 
  flies 
  — 
  too 
  many 
  to 
  mention 
  

   in 
  detail. 
  The 
  lake 
  shore 
  is 
  the 
  most 
  favoured 
  of 
  them 
  all, 
  but, 
  in 
  general, 
  they 
  

   follow 
  quite 
  closely 
  the 
  line 
  separating 
  sunlight 
  from 
  shadow. 
  

  

  The 
  flies 
  are 
  averse 
  to 
  penetrating 
  shadow, 
  unless 
  sunlight 
  is 
  perceptible 
  beyond, 
  

   and 
  even 
  more 
  averse 
  to 
  crossing 
  sunlit 
  spaces 
  unless 
  shadow 
  or 
  massive 
  shelter 
  

   is 
  perceptible 
  beyond. 
  

  

  * 
  It 
  was 
  not 
  necessarily 
  unattractive 
  shelter 
  that 
  prevented 
  the 
  males 
  from 
  

   congregating 
  at 
  these 
  particular 
  points. 
  They 
  were 
  distant 
  from 
  all 
  sources 
  of 
  food, 
  

   and 
  however 
  attractive 
  shelter 
  may 
  have 
  been 
  (it 
  was 
  in 
  fact 
  very 
  attractive 
  at 
  49 
  and 
  50, 
  

   but 
  not 
  at 
  41) 
  no 
  permanent 
  concentration 
  of 
  males 
  could 
  occur. 
  

  

  The 
  males 
  tended 
  to 
  congregate 
  at 
  point 
  46, 
  which 
  was 
  well 
  sheltered 
  ; 
  but 
  not 
  at 
  

   point 
  44, 
  just 
  the 
  other 
  side 
  of 
  the 
  creek, 
  where 
  shelter 
  was 
  not 
  attractive. 
  But 
  by 
  

   the 
  time 
  the 
  relatively 
  idle 
  males 
  had 
  dispersed 
  much 
  beyond 
  point 
  46, 
  towards 
  points 
  

   49 
  and 
  50, 
  they 
  began 
  to 
  require 
  food, 
  and 
  there 
  was 
  no 
  food 
  unless 
  they 
  passed 
  back 
  

   to 
  point 
  45, 
  or 
  passed 
  far 
  beyond 
  point 
  50. 
  

  

  In 
  other 
  words, 
  a 
  reach 
  of 
  foodless 
  shore, 
  although 
  supplied 
  with 
  both 
  shelter 
  and 
  

   breeding 
  ground, 
  produces 
  the 
  same 
  falling 
  off 
  in 
  male 
  density 
  and 
  elevation 
  of 
  female 
  

   percentage 
  as 
  the 
  shelterless 
  shore 
  described 
  in 
  the 
  pages 
  preceding 
  this. 
  

  

  