196 PARASITIC AMOEBAE OF MAN. 



these species differ from one another, as observed 

 in fresh preparations. 



Cytoplasm. The very marked distinction be- 

 tween the ectoplasm and the endoplasm in Entamoeba 

 histolytica and Entamoeba tetragena is one of the 

 most important features differentiating them from 

 Entamoeba coli. This distinction can always be made 

 in the motile organisms, and very frequently, in the 

 case of Entamoeba histolytica, when it is motionless. 

 The ecto- and endoplasm in Entamoeba coli can 

 hardly be distinguished even when the organism is 

 moving and never present the glass-like appearance 

 observed in the other species. 



Nucleus. In Entamoeba coli the nucleus is 

 almost always visible, situated near the centre of the 

 organism, and containing much chromatin, while it is 

 bounded by a very thick, well defined nuclear mem- 

 brane. In Entamoeba histolytica the nucleus is gen- 

 erally invisible, and when visible, is situated near the 

 periphery of the organism; contains but little 

 chromatin; and has no definite nuclear membrane. 

 In Entamoeba tetragena the nucleus is generally 

 visible; is large; contains much chromatin; and has 

 .a well defined nuclear membrane. It is distinguished 

 from the nucleus of Entamoeba coli by the broad 

 liyaline area surrounding the centriole and by the 

 cyclical changes occurring in the karyosome during 

 reproduction. 



