530 Universitu of CaJifornia, Publications in Zoology [Vol.20 



3. Councilmania muris is characterized by the formation of hyaline 

 pseudopodia ; by a central, diffuse karyosome ; by the occurrence of 

 numerous and massed chromatoidal bodies having irregular ends in 

 the mature cysts, by the frequency of chromophile ridges, by budding 

 cysts in stools, and by the presence of six chromosomes. 



4. Councilmani^i dccumani is characterized by the formation of 

 hyaline pseudopodia ; by a fairly distinct nuclear membrane, heavily 

 encrusted with chromatin material ; by an excentric, diffuse karyosome, 

 .somewhat more mas.sed than the karyosome of C. muris; by the pre- 

 sence of relatively few chromatoidal bodies which have a tendency to 

 form rounded ends; by the relative rarity of well defined chromophile 

 ridges ; and by the process of budding of cysts in the stools. 



5. Endamoeba ratti is characterized by the possession of granular 

 and vacuolated pseudopodia ; by a distinct nuclear membrane upon 

 which the chromatin has a tendency to be encrusted in a regular ring 

 or small beads; by chromatoidal bodies which resemble those of C. 

 mu7-is; and apparently by the absence of the budding process. 



6. Distinct size races of Councilmania muris and Councilmania 

 decumani have been observed, those of C. muris being 14.5/i, lo.T/x, and 

 n.lfi, respectively, and those of C. decumani being lAfi, 15.5fx., and IT/x, 

 respectively. 



7. The process of mitosis has been worked out in detail for the 

 species C. muris and C. decumani. It resembles mitosis as already 

 described for C. lafieuri (Kofoid and Swezy, 1921) and for Enda- 

 moeba coli as described by Swezy (1922). C. muris possesses six 

 chromosomes while C. decumani has only four. These chromosomes 

 present recognizable and constant differences in form. 



8. Keproduction of parasitic amoebae may occur either by binary 

 fission of the motile amoebae, or by multiple fission following encyst- 

 ment, which is the most common method. Young amoebae are extruded 

 from the cysts of C. muris and C. decumani by a process of budding 

 through a pore in the cyst wall in the caecum and stools by a process 

 similar to that described bj' Kofoid and Swezy (1921) for Coimcil- 

 mania lafleuri. No evidence of buds has been found to date for Enda- 

 moeba ratti. 



9. The possibility of the establishment of immunity to amoebic 

 infection by the rodent host is suggested by the facts that the incidence 

 of amoebic infection is higher in younger animals than in old ones, 

 that rats and mice may clear themselves of amoebic infection without 

 apparent treatment, and that it has been difficult to establish an 



