HOST-PARASITE RELATIONS: INTESTINAL PROTOZOA 



from 30 to 60 cm. posterior to the stomach, and within 

 about 40 minutes after the cysts were injected into the 

 stomach. The process was studied in the living organ- 

 ism and also on prepared slides. Activity within the cyst 

 is stimulated by unknown factors and the organism can 

 be seen moving about apparently by means of its axo- 

 styles. The cyst wall at the posterior end seems to become 

 weakened and the posterior end of the animal, which 

 has assumed the approximate shape of the trophozoite, 

 breaks through. Cysts were observed with only the pos- 

 terior flagella extruded; these were active and moved 

 the entire cyst about in the medium. Then the organism 

 gradually squeezes through the opening at the posterior 

 end. Division of the organelles occurs before the tropho- 

 zoite emerges but actual division takes place after it 

 becomes free. In all those observed the four nuclei re- 

 mained at the anterior end and did not separate into two 

 pairs, one pair at either end, as stated by Wenyon ( 1926). 

 Cell division proceeded from the anterior end posteriorly, 

 the organism, during the process, moving about by means 

 of the posterior flagella and the other flagella that ap- 

 peared to be forming. The excysted trophozoites after 

 division measured from 8.5 juto 10.5 ju in length (average 

 about 9. 5 n) and from 4.5 /x to 7 a in breadth (average 

 about 5.5 m). 



Wenyon (1926) suggests that cysts may excyst in the 

 same host in which they are formed ; this would account 

 for the increase in the number of specimens present in 

 the host, since division during the trophozoite stage 

 seems to be rare, but does not appear probable to the 

 writer. 



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