^^-■i] KfsscI: Amoebae of Culture Hats and Mice 52!) 



ill size. Exact chromosome counts, however, have been made and 

 these are important in differentiation of species. The chromosomes 

 found ill the parasitic amoebae are relatively small and simple when 

 compared with the chromosomes of the Metazoa. They are for the 

 most part small spheres or ellipsoids. In this investigation we have 

 found evidence of the precocious splitting of the chromosomes as 

 described by Swezj^ (1922) for Endamoeba coli. The chromosomes 

 do not retain their constancy of form during the resting stage of the 

 nucleus, but are reformed at each mitotic division from the chromatin 

 material scattered within the nucleus and encrusted upon the nuclear 

 membrane. It is probably because of insufScient observation of mitotic 

 stages of division that Wenyon (1922) seems to hold to the opinion 

 that "no definite chromosomes are formed during the division of the 

 nucleus" of parasitic amoebae. 



The formation of an intradesmose (Kofoid and Swezy, 1921) is 

 characteristic of the type of nuclear division in amoebae. This is 

 formed within the nuclear membrane and thus differs from the 

 paradesmose of the Mastigophora and from the centrodesmose of the 

 metazoan cell. 



SUMMARY 



1. The present investigation was begun in order to determine 

 whether or not rats may become infected with Endamoeba dysenteriae. 

 It was found necessary first to determine the amoebae that normally 

 inhabit the intestinal tract of rats and mice and this paper describes 

 the three species of amoebae found in the intestinal tract of culture 

 rats and mice. These three amoebae are : 



(a) Councilmania niuris, transferred from the genus Amoeba to 

 which it was assigned by Grassi (1881) and by Wenyon (1907). 



(6) Councilmania deeumani, transferred from the genus Enda- 

 moebato which it was assigned by Rudovsky (1921). 



(c) Endamoeba ratii sp. nov., found in only three of the rats dur- 

 ing the present investigation. 



2. Specifie differences of these amoebae are based on differences in 

 the structure of the protoplasm and pseudopodial formation, morpho- 

 logical differences in nuclear structure, in chromatoidal bodies, in the 

 formation of chromophile ridges, in the budding of cysts in the bowel 

 by which young amoebulae are discharged from the cyst, and on the 

 fact that the amoebae have been transferred by experiment from one 

 rodent to another without apparent racial or morphological change. 



