PARASITISM AMONG PROTOZOA 



105 



role, as in African sleeping sickness where the Trypanosomes 

 (Fig. 42, page 74) accumulate in the lymphatics, and, together 

 with attracted white blood corpuscles, block up the capillaries 

 and smaller arteries. When this happens in the base of the 

 brain, starvation and atrophy of the brain cells accompanied by 

 their loss of function result. This, in turn, is manifested by 

 characteristic lethargy, coma, and finally death. 



Representatives of all groups of protozoa have become 



Fig. 59— ADELEA OVATA 



A full-grown coccidian in an epithelial 

 cell of the intestine of the centipede. 

 The nucleus with its endosome is dis- 

 tinct. At the left is a group of spores 

 each with two sporozoites 



From a photomicrograph by the author 

 Magnification, 600 



adapted to parasitism and few animal types are free from them; 

 even protozoa themselves are subject to such infections! Para- 

 sitic flagellates and ciliates are widely distributed, the latter par- 

 ticularly in cattle and horses; rhizopods, with the exception of 

 ameba, are poorly represented among the parasites. 



Sporozoa 



In addition to the parasitic forms so far described, and also 

 in addition to the three types of protozoa — Mastigophora, Sar- 

 codina, and Infusoria — described in Chapter VIII there is a 

 fourth type of protozoa — the Sporozoa — made up of obligatory 

 parasites, not a free-living representative being known. These 

 forms are without motile organs. They reproduce for the most 

 part by means of encapsulated* spores, whereby protection is 

 assured against external conditions in passing from host to host. 



* Encapsulated, inclosed in a membrane or capsule. 



