690 MURIEL ROBERTSON. 
this middle stage of digestion. From such a range of forms 
it would be a simple matter to pick out creatures suggesting 
the morphological features which are considered character- 
istic of male and female individuals. Thus Pl. 17, figs. 23 
and 25, might be regarded as respectively male and female ; 
so also Pl. 17, figs. 24 and 26; but until the act of conjuga- 
tion is observed I cannot see that there is evidence enough 
to make it clear that the quite obvious morphological differ- 
ence 1s the expression of a sexual differentiation. 
At this middle stage of digestion dividing individuals are 
of frequent occurrence. In Trypanosoma vittate un- 
equal division at this stage is the rule rather than the excep- 
tion. ‘lhe process is figured in Pl. 17, figs. 18 and 19, and 
the different character of the products 1s obvious. 
The new flagellum unquestionably grows out apart, and 
does not arise by sphtting off from the old one. The split- 
ting of the flagellum, as is well known, does occur in certain 
Trypanosomes; as, for instance, in '. grayi described by 
Prof. Minchin,! and it is of interest to find two such very 
different methods holding good in the group. 
The new flagellum in T. vittatee will start growing out 
from the kinetonucleus before it is obviously divided, though 
it is generally enlarged. A review of Pls. 16 and 17, figs. 
16—20, will demonstrate this question pretty clearly. 
As time goes on the nature of the infection undergoes a 
very marked change; the predominating type of ‘Trypano- 
some is now found to be a slender rather short form with the 
flagellum extending only to a short distance beyond the end 
of the body. The undulating membrane is very narrow. 
The tropho- and kinetonuclei have entered into close rela- 
tions with each other, and generally the kinetonucleus is 
just anterior though closely applied to the trophonucleus. 
Specimens are found with the kinetonucleus posterior, but 
these are few in number. ‘lhe gradual predominance of this 
type to the exclusion of practically every other can be 
1 « Trypanosomes in Tsetse flies and other Diptera,” ‘ Q. J. Mier. Sci.,’ 
vol, 52, 1908. 
