4 MANUAL OF HUMAN PROTOZOA 



tively by means of pseudopodia, flagella, and cilia respec- 

 tively. The fluid food substances are taken in throusb the 

 entire body surface, while the solid food particles may be 

 engulfed by pseudopodia or taken in through a permanent 

 opening, the cytostome. The osmotic regulation is also 

 carried on through the body surface in the majority, and 

 there occurs no contractile vacuole in the human protozoa 

 except in Balantidkim coli (Fig. 13, l). 



The trophozoite multiplies as a rule by binary fission 

 which produces two daughter individuals. The species of 

 Plasmodium however multiply by multiple division or 

 schizogony (Figs. 21, 22). In this, the nucleus divides re- 

 peatedly without cytoplasmic division so that several to 

 many nuclei are produced within a trophozoite, and finally 

 each nucleus becomes the center of a daughter individual. 

 When the parent body breaks up, there are formed many 

 daughter trophozoites. On this account, this type of tropho- 

 zoite is called a schizont. 



After multiplying a certain number of times, the tropho- 

 zoites of the protozoa which depend on man as the only 

 host and not transmitted by invertebrates, encysts. It be- 

 comes gradually less active, and secretes a resistant wall. 

 Thus the cyst (Fig. 1, 5-9) is formed. The cyst wall thus 

 produced protects the inner protoplasm against low tem- 

 perature, desiccation, and other unfavorable external con- 

 ditions which the cyst encounters after being voided in the 

 faeces from the intestine. When a cyst finds its way into 

 the digestive tract of man in food or water, excystment 

 takes place, and young organism emerges and develops 

 into the trophozoite. The encystment however does not 

 take place in forms such as Trypanosoma, Leishmania, 



