227 
described by Koch, are reported in Trypanosoma gambicnse ingested 
by Glossina palpal is .* 11 
( 0 ) We have observ ed similar forms to (5) and in 011c instance at 
least the fusion, we believe, of two living Trypanosoma gambicnse in 
blood from the gut of .1 Slomoxys. 
The arguments on neither side are conclusive, but we believe those 
to be far the stronger which support the existence of a sexual cycle 
m the life history of the mammalian trypanosomes, possibly in the 
tsetse fly. 
It is, we believe, by the most patient and long-continued observation 
of living, individual parasites in trypanosome-containing blood 
(probably freshly ingested) from the gut of tsetse flies that a definite 
answer can best be given to the whole question. The work should be 
done under natural conditions in Africa and, naturally, the observations 
on living parasites must be controlled and supplemented by the study 
of stained specimens. The observer must approach the subject in a 
receptive mood and freed from preconceptions. 
VI. CONCLUSIONS 
from the consideration of all the facts we state the following 
propositions: 
It is known that, 
(0 Mammalian trypanosomes may be mechanically transmitted by 
l * le ' 3 * tes °f blood-sucking arthropoda. 
^ ( 2 ) A cycle of development of the trypanosomes exists in which 
° CCUr spherical parasites formed by the throwing off of blepharoplast, 
Undulati ng membrane and flagellum. These forms exist in both the 
'ertebrate and the vertebrate hosts; conjugation probably plays no 
£!l^he_pr oduction of this form. A possibly distinct cycle i s 
also describe “ ^ trypanosomes "• J OCC )! 5 r he^entirely e distinct 
,r °m the mam 1Ch i’ m common with N'ovy (23), they consider to recognisable 
as other th a mn ?u ,an tr . v panosonies. We have not seen trypai ( i nsta n C e, we 
f ound irvrri n 1 * lf,se 'ingested, in the Hies examined by us. , . but fresh 
marn 'Oal?an ^ SOI V eS in lhe 8"’ " f a freshly-caught Glosano flagellate, 
Was also nro b °° d was also present; another parasitic proto a > > w hich leads 
Minchin P e «f em - These Ay trypanosomes (aof have an encysted host> 
and s o take ,,,l ‘ir cysts may be excreted, iftgcsted interesting 
,ine; iSStK m a “contaminative cycle.” The hypothesis is a most ^ of 
v e,s e flie. s PY n s f a,es that the sexual forms of T. gambicnse o not be found. 
N '°thincr ..^tned disappeared and after 96 hours parasites rts 0 f the flv 
eita mined lat eni ^]| n 8 a trypanosome” was found in the ' arl ,' ' ^ t b e copula of 
lr - v Panosorn ’ ^ Wh y should developmental forms or the product ot 
oe trypanosome-like in shape? 
