398 ALDO CASTELLANI AND ARTHUR WILLEY. 
times the blood is literally seething with them, and it is 
known that they may equal or surpass the corpuscles of the 
blood in number. Like Hemogregarina, the Trypano- 
soma is chiefly met with in domesticated or semi-domesti- 
cated animals. We have not found it in birds, but have met 
with it in several species of freshwater fishes occurring in the 
Colombo Lake, a sheet of water in the heart of the town. 
One of the principal hosts is the siluroid fish, Sacco- 
branchus fossilis; most of the individuals of this 
species in the Colombo Lake, from seven to about twelve 
inches in length, appeared to be infected with a species 
of Trypanosoma, which we will name, in accordance with 
the method adopted by MM. Laveran and Mesnil, T. sacco- 
branchi. Here, as in the rat, the parasites vary greatly 
in number in different individuals, from very rare to very 
numerous. In a fresh hanging drop the parasites appeared 
two or three in the field of the microscope ; about two hours 
later those near the edges of the drop had begun to slow 
down, so that the movements of the undulating membrane 
could be observed. These consisted of a rapid shivering 
along one side of the body. The movements of the mem- 
brane determine the serpentine convolutions of the body, 
which are perpetual. Sometimes the body rests moment- 
arily, only the flagellum and anterior portion keeping up 
their movements. 
Four or five hours later bacteria had penetrated the entire 
drop, but in a portion of the latter where the bacteria were 
particularly dense the Trypanosomes had collected together, 
as many as twenty being visible at a time in the field of the 
microscope, a few only being found elsewhere in the drop. 
In their recent monograph on ‘ Trypanosomes et ‘Trypano- 
somiases,’ Paris, 1904, MM. Laveran and Mesnil have 
shown how difficult, and in some cases impossible, it is to 
distinguish one species of Trypanosoma from another on 
morphological grounds. There is the greatest possible simi- 
larity of structure and proportions between the Trypano- 
soma of rats and those of fishes. Such points as the position 
—-+- 2 — = =. —_—_— 
