301 
of the developmental forms of a Vertebrate Trypanosome producing 
cysts in the Insectan host, for expulsion to the exterior. But in the case 
of Trypanosoma grayi, in GI. palpalis, it is not improbable, I think, 
that we have such an instance. It may be pointed out that among the 
figures given by Kleine and Taute® of the forms of 7. gray: in the 
tsetse-fly, which were proved by the authors to be derived from the 
Trypanosome in the crocodile, there are two (figs. 65, 67) of the slender, 
(so-called) herpetomonad type, which were shown by Minchin? to give 
| rise to the cysts. The German workers, it is true, did not observe any 
actual cyst-formation. Just as “Crithidia” fasciculata has been seen 
many times, however, when the cysts have not been found, so it has been 
with 7. grayi; thus Roubaud!° only found cysts on 13 out of 30 occa- 
sions, in tsetses infected with 7. gray’. The last-named author confi- 
dently assumes that this parasite is purely an Insectan form, but the 
series of forms which he figures agree entirely both with those given by 
Minchin and with those given by Kleine and Taute, — forms which 
in my opinion do not resemble the types of form generally found in the 
herpetomonads or trypanosomids of Insects. 
There is an important hypothetical point which may be mentioned 
in this connection. The formation of cysts by a parasite occurring In a 
blood-sucking Insect does not necessarily mean that this parasite in un- 
connected with a Vertebrate Trypanosome. For in the case of a Try- 
panosome derived originally from an Insectan Flagellate, one which 
most probably formed cysts for its transmission from Insect to Insect 
(or larva), it is quite comprehensible that in certain cases this primitive 
mode of transmission may have been retained, in addition to the (second- 
ary) method of transmission by inoculation to the Vertebrate (or possibly 
even without the latter), where this course proved advantageous to the 
species. If “Crithidia” fasciculata is really the developmental form of 
a Trypanosome, such an explanation would account for the presence of 
resistant cysts. Of course, this is nothing more than a hypothesis so far; 
but it is interesting to note that a similar view has been suggested by 
Chagas", in his account of Trypanosoma (Schixotrypanum) cruxt. He 
puts forward the possibility of the infection of fresh bugs (Conorhinus) 
by means of the excrement of infected ones, and is inclined to suppose 
this may be effected by the “crithidial” forms of the parasite (without 
the occurrence of actual cysts being suggested). 
In conclusion, although the fact of the occurrence of cysts in 
8 Arb. kais. Gesundheitsamt, 31. 1911. S. 321. 5 pls. 
9 Quart. Journ, micr. Sci., 52. 1908. p. 159. 6 pls. 
10 C. R. Soc. Biol. 72. 1912. p. 440. 
11 Mem. Inst. Oswaldo Cruz, 1. 1909. p. 159. pls. 
