PROTOZOA IN THE DIGESTIVE TRACT 17 



nucleus is characterized by a thicker membrane than that 

 of E. histolytica. The peripheral chromatin granules are 

 coarser and often in block-form, and the endosome is a 

 much larger body, about lu in diameter, and located usual- 

 ly eccentrically. The clear ring around the endosome may 

 be narrow or wide, and smaller chromatin granules may 

 be lodged on the achromatic network present in the nu- 

 cleoplasm. The nucleus is about 5-8m in diameter. Although 

 the typical nucleus of this amoeba is quite different from 

 that of E. histolytica, there occur invariably atypical or 

 degenerating individuals with nuclei which may appear 

 intemiediate between the two. If undecided, one must look 

 for many typical individuals in which a positive identifica- 

 tion can be made. 



Precystic forms 



Prior to encystment, the amoebae (Fig. 2, 6) become 

 much smaller through division and transform themselves 

 into precystic amoebae. These are usually rounded and 

 more sluggish than the trophozoites. The cytoplasm does 

 not contain food material. The amoeba resembles closely 

 that of E. histolytica, but may be slightly larger. It is 

 8-20m in diameter. The nucleus shows a typical appearance, 

 but may show a structure somewhat resembling that of 

 £. histolytica. Therefore, it is quite difficult, as was stated 

 already, to differentiate the two species of Entamoeba in 

 precystic forms. 



Cysts 



1. Living specimens. The cyst (Fig. 2, ") is usuallv 

 spherical, but often ovoid in form. It measures 10-30m in 



