ENDAMCEBA CITELLI SP. NOV. 445 



resists digestion. This will be discussed below. No red blood 

 corpuscles or tissue cells were ever observed within the cytoplasm. 

 These facts make it fairly safe to conclude that the amoeba is a 

 commensal and not a true parasite. 



The locomotion of the free forms was studied, because the 

 character of pseudopod formation has come to be of so much im- 

 portance in correct classification (Dobell, 1921, Kofoid, Swezy, 

 and Kessel, 1923). When kept slightly warmed they exhibited 

 great activity with frequent pseudopod formation. The pseudo- 

 pods were clear and broadly rounded. The endoplasm did not 

 invade them after they were formed, but they were often with- 

 drawn before the endoplasm had completely filled them. They 

 were not, however, thrust out with the explosive suddenness 

 characteristic of Endamceba histolytica which the writer has been 

 fortunate enough to observe on several occasions. Typical 

 "fountain streaming" or limax movement was observed in a 

 number of individuals. The nucleus is not prominently visible 

 in the living specimens, but it can be made out after observing 

 the amoeba carefully for a while. 



Measurements of stained specimens of the free amoebae show 

 considerable variation. The smallest one measured eleven by 

 ten micra, and the largest twenty-three by twenty-five micra. 

 An average of ten amoebae measured was fifteen by sixteen micra, 

 which is somewhat smaller than either Endamceba coli or Enda- 

 mceba histolytica, but compares favorably with Kessel's (1924) 

 measurements of Councilmania decumani from mice and rats. 

 The nuclei of the free forms measure from four by four micra to 

 six and one tenth by five and two tenths micra in size. Ten 

 measurements averaged four and nine tenths by four and eight 

 tenths micra, which is slightly smaller than the figures given for 

 E. histolytica and E. coli. (Hegner and Taliaferro, 1924.) 



The nucleus is definitely of the vesicular type, with a deeply 

 staining karyosome which varies in position from central (Fig. 6) 

 to extremely excentric (Fig. i). Usually it is less pronouncedly 

 excentric, as in Fig. 2. This karyosome is surrounded by a 

 clear achromatic zone, which in turn is surrounded by a layer 

 of more or less concentrated slightly basophilic substance (Figs. 

 1-6; 8). Between this layer and the nuclear membrane is an 



