28o 
marked  at  the  south  end  of  Lake  Tanganyika  and  the  north  end  of 
Lake  Nyasa,  where,  in  both  cases,  it  occurs  almost  at  the  water's 
edge.  At  the  south  end  of  Lake  Nyasa  and  in  the  neighbourhood  of 
Lakes  Mweru  and  Bangweulu,  the  slope  is  more  gradual,  and  the  level 
of  the  plateau  is  only  reached  at  a  distance  of  forty  or  hfty  miles 
from  the  river. 
Neave*  has  reported  that  the  occurrence  of  Glossina  palpalis  oxi 
several  of  the  rivers  in  the  Katanga,  stops  rather  suddenly  about 
1 0°30'  S.,  in  some  cases  coinciding  with  the  abrupt  rise  to  the  plateau 
level.  On  the  Luapula  river  no  such  marked  transition  occurs  ;  indeed 
the  drop  between  Lake  Bangweulu  and  Lake  Mweru  is  only  some 
seven  hundred  feet  (3,700-3,000  ft.),  but  the  stoppage  of  the  fly  at 
about  ii°30'  S.  corresponds,  more  or  less,  with  a  change  in  the 
vegetation  of  the  river  banks.  North  of  that  latitude,  the  banks  are 
fairly  well  wooded,  while  south  of  it,  the  river  runs. for  long  stretches 
through  bare,  flat  country,  and  this  probably  has  acted  as  a  bar  to  the 
extension  of  Gl.  palpalis  to  Lake  Bangweulu  and  the  Chambesi 
Valley. 
Neave  also  suggests  that  the  absence  of  GL  palpalis  from  the 
greater  part  of  Rhodesia  and  Nyasaland  may  be  due  to  the  change 
in  the  fauna,  which  occurs  in  this  portion  of  Africa,  from  the  West 
Coast  type  to  that  of  the  Eastern  and  Angolan  regions.  Apparently 
this  species  of  fly  oversteps  the  boundary,  for  it  was  captured  on  the 
Zambesi,  between  Tete  and  the  Victoria  Falls,  by  Sir  John  Kirk.t 
Since  the  conditions  on  Lake  Nyasa,  on  the  Luangwa  river  and  on 
other  tributaries  of  the  Zambesi  are  quite  favourable  for  the  existence 
of  GL  palpalis,  it  is  very  important  to  ascertain  as  soon  as  possible 
whether  it  is  still  to  be  found  anywhere  along  this  system  of  waters, 
Altitude  is  unfavourable  to  the  development  of  GL  palfaln, 
probably  on  account  of  the  temperature.  According  to  Roubaud+  the 
most  suitable  temperature  varies  between  25°  and  30°  C.,  and  on  the 
plateau  the  mean  is  lower  than  this.  At  Kambole,  on  the  Tanganyika 
plateau  (about  4,800  feet  above  sea  level)  where  careful  records  were 
kept  for  some  years,  the  mean  daily  temperature  was  found  to  be 
21°  C.,  and  the  variation  between  7'2°  and  32'2°  C.  These  conditions 
*  Neave,  1908.  Report  of  Katanga  Medical  Commission,  Ixindon. 
t  Austen,  1903.  Monograph  of  the  Tsetse  flies, 
t  Roubaud,  1908.  Bulletin  Soc.  Pathologic  exotique,  T.  I,  No.  5. 
