326 
periodically.  In  March,  1908,  we  followed  the  fresh  spoor  of  three 
different  herds,  and  on  no  occasion  did  we  encounter  any  Glossina. 
An  answer  to  this  question  might  be  given  if  the  diet  of  Glossina 
could  be  satisfactorily  determined.  It  is,  we  believe,  agreed  that 
other  blood-sucking  Diptera--Culicidae,  Tabanidae,  and  the  related 
genera  of  the  Muscidae,  Slomoxys,  Haematobia  and  Lyperosia  can 
exist  without  blood ;  but  it  is  commonly  held,  and  Austen  has 
recently  emphasised  his  belief  in  this  view,  that  Glossina  demands 
blood  and  will  not  exist  on  plant  juices.  This  writer  bases  his 
argument  on  the  high  specialisation  of  the  genus ;  other  writers, 
notably  those  from  south  of  the  Zambesi,  on  the  rumoured 
inseparability  of  fly  and  ‘game.’  F.  J.  Jackson,^  Stordy,t  and  other 
observers  in  East  Africa,  Sir  Alfred  Sharpe  and  Harger  in  Nyasaland 
and  Northern  Rhodesia,  have  failed  to  notice  any  intimate  connec¬ 
tion,  and  our  own  work  supported  this.  The  extraordinary  number 
of  Gl.  morsitans  (almost  incredible  to  one  who  has  not  been  in  their 
haunts)  in  many  cases  where  ‘  game  ’  is  exceedingly  rare,  would 
appear  to  preclude  the  possibility  that  more  than  a  small  percentage 
could  obtain  a  mammalian  blood  meal,  at  what  one  may  suppose  to 
be  satisfying  intervals.  It  is  recognised  that  in  captivity  a  tsetse 
must  as  a  rule  be  fed  at  least  every  forty-eight  hours ;  in  nature  it 
would  often  seem  impossible  for  more  than  one  or  two  per  cent,  to 
feed  on  blood,  say,  every  six  or  ten  days  ;  in  some  cases,  owing  to  the 
entire  absence  of  any  game  indications,  it  would  certainly  look 
dubious  if  within  a  dry  season  the  majority  could  get  a  blood  meal. 
Sir  Alfred  Sharpe  in  a  private  letter  mentions  that  he  had  often 
been  struck  by  the  great  preponderance  of  flies  which  on  crushing 
apparently  contained  no  blood. 
We  have  never  been  able  to  keep  captive  flies  alive  for  more  than 
ninety-six  hours  after  feeding,  but  up  to  that  time  there  was 
invariable  evidence  of  the  meal.  Certain  variations  in  the  rate  of 
digestion  were  seen  :  in  a  few  flies  no  corpuscles  remained  after 
thirty  hours,  in  others  they  were  seen  intact  after  seventy-two. 
Following  the  disintegration  of  corpuscles  the  gut  contents  become 
granular  and  darker,  and  pigment  grains  are  seen  m  the  cells  lining 
*tF.  J.  Jackson  and  K.  Stordy.  vide  Austen’s  Monograph  of  tsetse  ftw> 
London,  1903,  pp.  295-  29’ • 
