CHAPTER IX 
ARTHROPODS AS ESSENTIAL HOSTS OF PATHOGENIC PROTOZOA 
Insects and Trypanosomiases 
By trypanosomiasis is meant a condition of animal parasitism, 
common to man and the lower animals, in which trypanosomes, 
peculiar flagellate protozoa, infest the blood. Depending upon the 
species, they may be harmless, producing no appreciable ill-effect, 
or pathogenic, giving rise to conditions of disease. A number of 
these are known to be transferred by insects. 
In order that we may 
consider more fully the 
developmental stage of 
these parasites within 
their insect host, it is 
necessary that we des¬ 
cribe briefly the structure 
of the blood-inhabiting 
stage. 
The trypanosomes are 
elongated, usually point¬ 
ed, flagellated protozoa 
(fig. 136) in which the 
single flagellum, bent 
under the body, forms the 
outer limit of a delicate undulating membrane. It arises near 
one end of the organism from a minute centrosome-like body 
which is known as the blepheroplast, and at the opposite end extends 
for a greater or less distance as a free flagellum. Enclosing, or 
close beside the blepheroplast is the small kinetonucleus. The 
principal nucleus, round or oval in form, is situated near the center 
of the body. Asexual reproductions occurs in this stage, by longi¬ 
tudinal fission, the nucleus and the blepheroplast dividing independ¬ 
ently of one another. From the blepheroplast of one of the daughter 
cells a new flagellum is formed. 
Among the pathogenic species are to be found the causative 
organisms of some of the most serious diseases of domestic animals 
and even of man. It is probable that these pathogenic species secrete 
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