N. H. SWELLENGREBEL AND C. STRICKLAND 
375 
going to divide it becomes much broader (Diagram XI, Figs. 20—23) 
when the blepharoplast and nucleus divide (Fig. 22) a new flagellum 
is formed alongside the old one (Fig. 23) and at last the whole cell is 
divided (Fig. 24). 
In the non-dividing forms two types, a slender and thick one, may 
be distinguished (Figs. 18—19), but this dimorphism has now been so 
often found that we do not think it has any special significance. In 
Fig. 14 (Diagram X) a very large type, which hardly deserves the 
name “ Small trypanosome,” is drawn; we do not understand its 
significance but merely mention it because it was sometimes en¬ 
countered. 
That the small trypanosomes are really directly connected with the 
small oval forms and Crithidiae is shown also in Fig. 16 (Diagram X) 
which represents a rosette showing dividing and small oval forms 
(a) intermediate forms between small oval forms and crithidiae, ( b ) a 
stout crithidia, (c) and two forms of which one is a slender crithidia, 
and the other an intermediate form between this one and the small 
trypanosome, ( d ) corresponding with Fig. 16 (Diagram XI). 
These small trypanosomes are particularly interesting because they 
resemble the forms found by Chagas in the salivary glands of Conor- 
rhinus infected with Schizotrypanum cruzi. There is however the 
great difference (apart from the place they occupy in the invertebrate 
host) that T. lewisi exhibits only one sort of development leading to 
the formation of the small trypanosomes, whereas in Schizotrypanum 
these forms are produced by a special development, different from that 
producing only crithidiae and round forms which are considered by 
Chagas to be merely cultural forms. 
This was the last stage of development we found ; neither in the 
Series F nor in fleas taken haphazard from the infected rat at different 
times could we find anything beyond this stage. 
Comparison with cultural forms. Diagram XII shows some of the 
characteristic forms out of a culture of T. lewisi on Novy and MacNeal’s 
medium. Figs. 1—3 are large and small crithidiae. Figs. 1 and 2 
show very distinctly the mode of division of the flagellum ; only the 
basal part is divided and so a short flagellum is formed which grows 
out. Figs. 4—8 show round forms in different stages of division. The 
blepharoplast first divides and seems to play the part of a centrosome 
during the subsequent division of the nucleus in the same way as 
described by Franga, but we think that, at least in this case, this 
function of blepharoplast is only an apparent one because sometimes 
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