660 
In regard to their action on animals, the members 
of this group may be said generally to affect many 
different species of animals—as, for example, man, 
horses, cattle, dogs, and most of the smaller experi- 
mental animals, The two Central African members 
of the group, T. brucei and T. gambiense, develop in 
the tsetse-flies in the same way. At first the develop- 
ment takes place in the intestine; afterwards the 
parasites pass into the salivary glands, by way prob- 
ably of the proboscis, and there complete their develop- 
GR. BR gist. 


Zululand, 1973. 
Fic. 1.—T+yfanosoma brucei (Plimmer and Bradford) 
xX about 700. 
ment into infective forms. This is the only group in 
which the salivary glands are invaded. This group 
can be separated from the other groups by shape 
alone. 
Group B. The Trypanosoma pecorum Group.—The 
trypanosomes are small and monomorphic. The cyto- 
plasm is non-granular. The micronucleus is pro- 
minent, subterminal, and often seems to project 
beyond the margin. |The undulating membrane is 
fairly well developed (Fig. 2). 
The cycle of development in the tsetse-fly in Group B 
begins in the intestinal tract; afterwards the flagel- 
lates pass forward into the proboscis of the fly, and 
finally reach the salivary duct or hypopharynx, where 
they complete their development and become infective. 
The difference between Group A and Group B is that 

Fic. 2.—T7yfanosoma pecorum. 
Xabout 700. 
in the latter the salivary glands are never invaded. 
There are only two species at present included in this 
group—T. pecorum and T. simiae. The former gives 
rise to the most important trypanosome disease: of 
cattle in Africa, while the latter is remarkable for the 
rapidity with which it kills the domestic pig. 
“Group C. The Trypanosoma vivax Group.—The 
species making up this group (Fig. 3) are mono- 
morphic, and remarkable for the extreme rapidity 
of their movements. The posterior extremity is en- 
larged. The cytoplasm is clear and hyaline. The 
NO. 2389, VOL. 95] 
NATURE 

[AUGUST 12, 1915 

; micronucleus is large and terminal, and the undulating 
membrane is little developed and simple. This species 
only affects horses, cattle, goats, and sheep. Monkeys, 
dogs, rabbits, guinea-pigs, and rats are refractory. 
The cycle of development in Group C differs from 
that in Groups A and B in that it takes place at first 
only in the labial cavity of the proboscis, and later 
in the salivary duct or hypopharynx. No part of the 
cycle takes place in the intestinal tract or in the 
salivary glands. 
These three groups are well marked, and it is fairly 
easy by microscopic examination alone to name what 
group a trypanosome belongs to, when seen in the 
blood of the vertebrate host or even in the tsetse-fly. 
DESCRIPTION OF THE TSETSE-FLIES. 
A description of Glossina morsitans and Glossina 
palpalis is given, with a figure illustrating the mouth 
parts of a tsetse-fly. 
It is important to understand the structure of the 
proboscis, as this plays an important part in the 
development of Groups B and C. In the transverse 
section the parts are seen in position, the labrum and 
labium joined together form a tube through which 
the blood is drawn in the act of sucking, and known 
as the labial cavity; and the delicate terminal duct of 
the salivary glands or hypopharynx lying in the hollow 
of the labium, and opening near the tip of the pro- 
boscis. The salivary glands are long convoluted 

xal out 700. 
Fic. 3.—Tryfanosoma vivax (Ziemann). 
organs lying chiefly in the abdominal segment of the 
It. was stated that probably all the tsetse-flies are 
capable of acting as carriers of all the pathogenic 
trypanosomes, at least in laboratory experiments. 
What makes one species of fly the especial carrier of 
a particular trypanosome is probably bound up in the 
natural history, the habits, and distribution of the fly. 
It was shown that the two principal groups of tsetse- 
flles—the G. morsitans group and the G. palpalis 
group—differ from each other in well-marked char- 
acters, the former living in wild, unpopulated districts 
and trusting to the wild game for their. food, the latter 
along rivers and lakes which are usually thickly popu- 
lated, and trusting to man fora food supply, or in his 
absence living on the large reptiles, birds, and ante- 
lopes which frequent these places. 
THE TRYPANOSOMES CAUSING DisEasE IN MAN AND 
Domestic ANIMALS IN CENTRAL AFRICA. 
Group A. Trypanosoma brucei Group. 
(1) T. brucei, the Nagana Parasite.—This was the 
first pathogenic trypanosome discovered in Central 
or South Africa. It was found in Zululand in 1894 in 
the blood of native cattle suffering from Nagana. 
, The parasite was sent in the living condition to the 
ee 
