SPORE-PRODUCING PROTOZOA 15 



Flagellates. They include widely differing forms, 

 such as the Euglena of pond -water, Prowazekia 

 (Fig. 2) occurring in urine, the parasites of human 

 sleeping sickness and cattle-fly disease, the trypano- 

 somes; while Trypanoplasma is a biflagellate para- 

 site of fishes and flat-worms allied to Trypanosoma. 

 Also, there are natural Flagellates found in many 

 insects. These Flagellates belong to the genera 

 Crithidia and Herpetomonas, and a form of the 

 latter is found parasitic in man, being responsible 

 for the loathsome diseases Kala-azar and Oriental 

 sore. One stage in the life-history of the parasite 

 causing these diseases is frequently known as the 

 Leishman-Donovan body, that name having been 

 given before the true relationship of this phase of 

 the organism was fully realized. The life-histories 

 of Trypanosoma, Crithidia, and Herpetomonas will be 

 discussed in detail later. 



Probably more or less allied to the Flagellata vera 

 are the Spirochaetacea, members of which are re- 

 sponsible for relapsing and tick fever, fatal alike to 

 human beings, cattle, and birds. 



The largest number of pathogenic agents among 

 the Protozoa is probably to be found among the 

 Sporozoa. This huge section of the Protozoa is 

 distinguished from the others by its members pro- 

 ducing resistant forms (spores) at some stage of 

 their existence by which they are enabled to with- 

 stand unfavourable conditions and ultimately to 

 find their way into other hosts. The Sporozoa 

 literally are the spore-producing animals. Among 

 them there is very great diversity of form, move- 



