516 



VniversUy of Calif ornm Puhlicatwns in Zoology [Vol. 20 



species of amoeba simulates very closely the movement of Endamoeba 

 coli as described by Dobell (1921), and Kofoid, Swezy, and Kessel 

 (19236). 



Endamoeha ratti, although possessing many of the characteristics 

 of E. coli, is smaller in size, the average diameter of rounded, unen- 

 cysted forms being about 19/^, while that of E. coli ranges from 20/x 

 to 30;a (Dobell and O'Connor, 1921). 



10 



Fig. C 

 Freehand sketch of Endamoeba ratti while in progressive movement. 



The nuclear membrane is definite and is encrusted with chromatin 

 which may present a beaded appearance or a darkly staining ring 

 (pi. 48, fig. 57). The karyosome is excentric and may be surrounded 

 by a clear or a gray halo (fig. 57). 



The food appears to be the same as that ingested by the other non- 

 pathogenic amoebae of the intestinal tract of rats and mice. 



ENCYSTMfcNT 



As permanent slides have been procured from only two cases of 

 infection of Endamoeba ratti, it has been impo.ssible to secure a com- 

 plete series of the developmental stages of the cysts. A sufficient num- 

 ber of the eight-nucleate cysts have been found to give a typical picture 

 of the ripe cysts, and a few of the intervening stages have been seen. 



