26o 
I.  INTRODUCTION 
The  following  notes  form  a  record  of  some  observations  which 
were  made  on  the  parasites  occurring  in  the  intestine  of  Glossina 
palpalis  and  in  the  intestine  and  proboscis  of  Glossina  morsilam. 
They  are  admittedly  scanty  and  incomplete,  as  we  were  able  to 
devote  only  a  very  short  time  to  the  work,  and  much  of  this  time  was 
disadvantageously  employed  through  the  non-receipt  of  literature 
bearing  on  what  had  already  been  done  on  these  protozoa. 
In  the  earliest  efforts  made  to  trace  a  developmental  cycle  of  the 
pathogenic  trypanosomes  in  the  tsetse  flies,  e.g.,  in  the  work  of  Koch,! 
and  Gray  and  Tulloch,^  the  not  unnatural  mistake  was  made  of 
considering  all  the  parasites  found  in  the  flies  to  be  derived  from  the 
pathogenic  forms.  As  a  result  of  further  work  done  in  conjunction 
with  Minchin,''^  Gray  and  Tulloch  admitted  that  their  earlier  con¬ 
clusions  were  erroneous,  and  about  the  same  time  Novy^  pointed  out 
the  possibility  of  the  same  thing.  Stuhlmann^  took  the  precaution  of 
working  with  laboratory-bred  flies,  but  in  a  recent  paper,  in  which 
the  whole  subject  is  reviewed,  Patton  and  Strickland®  consider  that 
sources  of  error  exist  in  his  experiments,  and  they  also  take  exception 
to  some  of  Mmchin’s^  results  and  to  those  of  Keysselitz  and  Mayer,® 
Roubaud,^  and  others. 
In  the  light  of  our  present  knowledge  of  the  wide-spread  infection 
of  many  arthropods  by  various  protozoal  parasites  there  are  some 
grounds  for  the  criticism  of  much  of  the  previous  work.  It  is 
therefore  apparent  that  in  approaching  a  subject  beset  by  so  many 
inherent  difficulties  the  greatest  care  must  be  exercised  in  the 
conduct  of  the  work  and  that  it  must  be  controlled  in  the  most 
complete  manner.  The  use  of  ‘  wild  ’  tsetse  flies  in  work  on  develop¬ 
ment  cannot  be  justified  on  any  ground  ;  for,  apart  from  the  presence 
of  benign  parasites  which  confuse  the  results,  there  exists  a  possibility 
that  they  may  be  naturally  infected  with  a  different  species  of 
trypanosome  from  the  one  which  is  being  employed  in  the  experi¬ 
ments.  Even  in  the  case  of  laboratory-fed  flies,  the  criticism  has  been 
made  that  sufficient  care  has  not  been  observed  to  exclude  the 
occurrence  of  a  hereditary  transmission  of  the  non-pathogenic 
parasites.  Minchin  and  Stuhlmann  dispute  the  possibility  of  this, 
while  Novy  and  McNeal  and  Patton  and  Strickland  think  that  it  may 
occur. 
