TRYPANOSOMES IN TSETSE-FLIES AND OTHER DIPTERA. 181 
rations, not only by their snake-like form, but also by the 
clearness of their cytoplasm, which is free from granulations, 
and remains scarcely, or not at all, tinged by the Romanowsky 
method of staining. Comparison of earlier stages show that 
these slender forms arise from the slender or intermediate 
forms met with in the blood before it is taken up by the 
fly, by absorption of the granules in the cytoplasm. The 
whole appearance of these forms suggests the activity and 
mobility which they are seen to possess when observed in the 
living state. The flagellum is very long and stands well off 
from the body, but the undulating membrane is not greatly 
pleated. The kinetonucleus is a circular dot usually placed 
at or very near the posterior end, but sometimes at a short 
distance from it. ‘The nucleus has a dense, compact appear- 
ance, and usually a compressed form, but very frequently an 
irregular outline, with sometimes an appearance as if portions 
of chromatin were being detached from it, as noted in my 
preliminary communication (fig. 56, and P. R.8., 878, Pl. XI, 
figs. 4, 5, and 6). 
The stout forms (figs. 46, 47, 49-51, 53-55, 60, 63-65, 76, and 
P.R.S., B78, Pl. XII, figs. 7-14), on the other hand, are large 
and obese, with cytoplasm coarsely granular and staining 
deeply. The flagellum is short, the undulating membrane 
but slightly pleated, and the kinetonucleus, which is circular 
or rod-shaped, is usually some distance from the posterior 
end, a point in which they contrast with the “stumpy ” 
forms found in the vertebrate body. Sometimes the posterior 
end is prolonged into a short “rostrum,” a feature which 
becomes exaggerated at a later stage. ‘The nucleus is large 
and loose in texture, but of definite outline, often with a 
peripheral ring of coarser granules, but never showing the 
appearance of chromatin being ejected, as in the slender 
forms. 
Not only do these two forms of trypanosomes differ in 
structure and appearance, they also show a curious difference 
in the mode of division. When the slender forms divide the 
two daughter-kinetonuclei keep close together at the posterior 
