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concomitant  factor,  wind,  unc|uestionably  influences  the  aiea  of  dis¬ 
tribution,  for  during  the  monsoon  the  fly  apparently  disappears  almost 
completely  from  the  exposed  places,  such  as  the  Loangwa  Machmgas 
already  mentioned,  and  is  carried  over  into  normally  clean  country. 
We  may  instance  in  this  connection  the  road  which  one  of  us  followed 
at  the  end  of  the  rainy  season  (March,  1908)  from  Kapata  at  the 
south  end  of  Lake  Bangueolo,  via  Kisengo  and  Kalasa  to  Sakontwi  on 
the  Luapula.  No  Glossina  were  encountered  until  reaching  the 
river,  but  all  the  villagers  en  route  were  agreed  that  in  the  windy 
season  of  each  year  (June  to  September)  they  frequently  catch  tsetse, 
and  they  believe  them  to  have  been  carried  across  from  the  perpetual 
zones  on  the  Luera  river,  a  distance  of  about  twenty  miles.  This  was 
supported  by  an  Official ;  but  it  is  to  be  admitted  that  the  fact  is 
susceptible  of  other  interpretations. 
The  chief  factor  concerned  in  the  distribution,  so  far  as  our 
observations  can  lead  us  to  a  conclusion,  is  the  nalure  of  the  country 
and  its  vegetation. 
The  Native  Commissioner  at  Sumbu  on  Lake  Tanganyika  has 
assured  us  that  on  more  than  one  occasion  he  has  taken  Glosstm 
morsiians  near  to  that  place,  in  the  middle  of  a  broad  grass  plain 
over  half  a  mile  in  width,  and  that  the  fly  rise  from  the  isolated  and 
insignificant  shrubs  which  grow  on  the  water-course  there.  This  is 
the  only  evidence  we  have  obtained  of  the  occurrence  of  morsitam 
away  from  bush  country;  though  the  flats  may  be  mentioned 
which  extend  from  Sakontwi  across  the  extreme  corner  of  the 
Congo  State  towards  Chitambo.  Here,  in  August,  1907,  one  of  us 
took  this  fly  from  around  the  tree-studded  ant  hills  which  crop 
up  in  the  bare  grass  plains  at  intervals  of  one  hundred  to  four  hundred 
yards.  To  a  greater  degree,  are  they  found  in  the  park-hke  country 
which  sometimes  fringes  the  true  bush  country,  and  connects  it  with 
the  larger  of  the  open  plains.  Here  the  trees  attain  greater  size  and 
substance,  but  are  set  at  such  distances  in  the  grass  that  the 
impression  recalls  a  private  park  in  Kngland. 
It  is  in  the  virgin  forest  or  bush  that  Glossina  morsiians  takes  a 
permanent  abode.  This  type  of  vegetation  covers  the  greater  part 
of  all  watersheds  and  high-lying  country,  being  broken  only  by  the 
grassy  ‘  dambos  ’  which  serve  as  drains.  These  dambos  or  open 
grass  plains  (vlei  of  the  Dutch)  commence  as  narrow  strips  of  thirty 
