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 

 (flg. 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 



136. Trypanosome brucei. After Bruce. 



