12 PROTOZOAN PARASITISM 



ence of a protozoon, it is the directing factor of its 

 activities, it carries the hereditary characteristics of 

 the species, and it naturally plays the essential role 

 in division and the production of offspring. It is 

 the directing force of somatic life and, at the same 

 time, the germ of the offspring. 



CHARACTERISTICS OF THE CYSTS 



Each encysting species has its own peculiar cyst, 

 the importance of which in identification of the para- 

 site is not as widely recognized and attended to as 

 it should be. Particularly is this the case in the two 

 intestinal amoebae of man between which it is of so 

 much importance in medicine to distinguish. 



The shape and size of protozoan cysts are char- 

 acteristic of the species, the contour being more nearly 

 rounded than in the vegetative phase and the size 

 usually reduced. The cyst wall or shell is of con- 

 siderable thickness in some and of less definiteness 

 in others. The body of the organism is condensed 

 and usually motionless after the stage is fully de- 

 veloped. The cytoplasmic division into ectoplasm 

 and endoplasm is not definite. The various organ- 

 elles of the vegetative phase are indistinct or not 

 seen. Undigested food bodies are absent but some 

 contain stored materials, such as glycogen. Some 

 contain ''chromidial" bodies, in the shape of slivers, 

 bars, or blobs, which take the nuclear stain. The 

 nuclei of the cysts are characteristic of the species, in 



