ENDAMOtBA COLI 



excyst in the intestine and give rise to four young 

 amoebae (see p. 88). 



Hyper parasitism. Both free-Hving and parasitic 

 amoebae are sometimes parasitized by other organisms. 

 One of these, a vegetable organism of the genus 

 Sphcerita, is known to invade the intestinal amoebae of 

 man. How destructive it is to its host, and whether it 

 plays a significant role in control, are points on which 

 we have no evidence. 



2. ENDAMCEBA COLI 



Trophozoite. The trophozoite of this species (Fig. 

 2a) also varies greatly in size but averages larger than 

 that of E. histolytica; it ranges from about i8/x to 40 ju 

 being usually 20fx to 30 in diameter. The ectoplasm is/x 

 meager in amount and not sharply separated from the 

 endoplasm ; the latter is very granular giving the organ- 

 ism a grayish appearance. Locomotion is sluggish and 

 no rapidly forming ectoplasmic pseudopodia occur. Food 

 vacuoles are usually abundant, containing bacteria and 

 various materials from the intestinal contents, but ordi- 

 narily no red cells or other tissue elements. Cleft-like 

 vacuoles sometimes appear. The nucleus is usually visible 

 in the living organism ; it is larger and coarser than that 

 of E. histolytica with a thicker membrane, more chroma- 

 tin on the membrane and a larger karyosome eccentrically 

 placed. 



Precystic stage. This resembles the similar stage of 

 E. histolytica but averages larger. 



Cyst. The cysts (Fig. 2b) range from lO/i to 30M or 

 more in diameter, the usual size being between 15^ and 



61 



o 



^''i^-f^t^ 



